Viessmann Vitodens 300-W Fault codes & diagnostics

156 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural GasLPG 19-35 kW 2010-present

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Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 50 High 46 Medium 59 Low
Just want the most common Viessmann Vitodens 300-W faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 156 documented codes

Tap any card for details

0F

Your boiler is currently set to maintenance mode, which usually means it is undergoing a service check or the service settings weren't exited correctly.

Low DIY-safe £0-80

What to check first

  1. Check if a heating engineer has recently worked on the unit and left it in service mode.
  2. Try to exit the service/maintenance menu using the boiler control panel 'back' or 'OK' buttons.
  3. Perform a simple reset of the boiler to see if it clears the status notification.

Related codes

Full explanation for 0F
5b:0

Your boiler has detected that your hot water cylinder is connected directly to the unit, but there is likely a communication error or a missing sensor signal prevent it from heating your water.

High Engineer only £120-250

Parts commonly replaced

  • NTC Cylinder Temperature Sensor
  • Sensor wiring harness
  • External connection H5 module

Related codes

Full explanation for 5b:0
5b:1

Your boiler has detected that the hot water cylinder is incorrectly positioned in the system's plumbing layout, which may cause inefficient heating of your water.

Low Engineer only £100-250

Parts commonly replaced

  • Pipework reconfiguration
  • NTC Cylinder Sensor

Related codes

Full explanation for 5b:1
6C:0 to 6C:100

Your boiler's internal pump or fan is not running at the speed required to circulate water or air correctly through the system.

High Engineer only £180-450

Parts commonly replaced

  • Circulation pump
  • Internal fan
  • Electronic Control Unit (PCB)

Related codes

Full explanation for 6C:0 to 6C:100
6C:100

Your boiler's hot water pump is working as hard as it can to move heat, but something is preventing the water from cooling down or circulating correctly.

Medium Engineer only £180-450

Parts commonly replaced

  • Internal DHW Pump
  • Plate Heat Exchanger
  • Electronic Control PCB

Related codes

Full explanation for 6C:100
6F:0 to 6F:100

Your boiler is providing an informational update about the maximum power level it is using to heat your hot water, rather than reporting a functional breakdown.

Low DIY-safe £0-80

What to check first

  1. No action is required as this is an advisory message indicating the power output setting.
  2. If hot water is too slow to heat, contact a professional to adjust the maximum output via the control unit.
  3. Restart the boiler to see if the notification clears from the display.

Parts commonly replaced

  • Boiler Control Unit
  • NTC Sensor

Related codes

Full explanation for 6F:0 to 6F:100
6F:100

Your boiler's computer memory card is telling the system to run at full power for hot water, which it cannot adjust or override.

High Engineer only £100-250

Parts commonly replaced

  • Boiler coding card
  • Main PCB

Related codes

Full explanation for 6F:100
7b:0

Your boiler is having difficulty communicating the correct time over its internal network system, which might affect your heating schedules.

Low DIY-safe £0-120

What to check first

  1. Check that the date and time settings on the main boiler control panel are correct
  2. Perform a simple reset of the boiler using the power button
  3. If you have a Vitotrol room thermostat, ensure it is powered and showing the correct time

Parts commonly replaced

  • None (Software reconfiguration)
  • LON communication module

Related codes

Full explanation for 7b:0
7b:1

Your boiler is having a minor communication issue where it cannot sync its internal clock with other connected heating components.

Low DIY-safe £0-80

What to check first

  1. Locate the main control panel and access the Menu.
  2. Go to Settings and find the Date/Time option.
  3. Manually reset the time and date to ensure the system updates its internal clock.

Parts commonly replaced

  • LON communication module
  • Internal battery backup

Related codes

Full explanation for 7b:1
7E:0

Your boiler has detected an incorrect setting regarding how its exhaust gases are vented, likely due to a setup error or a controller communication glitch.

Low Engineer only £80-160

Parts commonly replaced

  • Control Unit
  • Coding Plug

Related codes

Full explanation for 7E:0
Showing 11–20 of 156
7E:1

Your boiler is having trouble communicating with other boilers in its shared flue system, causing it to stop running for safety.

High Engineer only £120-280

Parts commonly replaced

  • Communication cable
  • LON module
  • Electronic control board
Full explanation for 7E:1
7F:0

Your boiler has detected an incorrect internal setting or a communication error between its electronic control boards.

High Engineer only £100-350

Parts commonly replaced

  • BCM board
  • Gas Valve Controller
  • Main PCB

Related codes

Full explanation for 7F:0
7F:1

Your boiler’s internal control system has encountered a rare hardware communication error that is preventing it from running properly.

High Engineer only £350-600

Parts commonly replaced

  • Main PCB (Control Unit)
  • Communication Module

Related codes

Full explanation for 7F:1
9A

Your boiler has lost its connection to the solar panel temperature sensor, meaning it cannot monitor how much heat is coming from your solar system.

Low Engineer only £120-220

Parts commonly replaced

  • Solar collector temperature sensor
  • Sensor wiring/connection cable

Related codes

Full explanation for 9A
9b

Your boiler has lost connection with one of its temperature sensors, meaning it cannot accurately monitor the water temperature to operate efficiently.

Medium Engineer only £120-£220

Parts commonly replaced

  • Cylinder temperature sensor
  • Flow temperature sensor
  • Wiring harness
Full explanation for 9b
9b:1 to 9b:127

Your boiler has detected an internal configuration error where the target temperature has been set to an invalid value or a internal circuit board fault is occurring.

Medium DIY-safe £180-450

What to check first

  1. Turn the boiler power off at the fused spur switch for 30 seconds and then back on.
  2. Attempt to reset the boiler using the control panel interface.
  3. Navigate to the heating settings and ensure the target temperature is set within a normal range (e.g., 40-75°C).

Parts commonly replaced

  • BCU (Boiler Control Unit)
  • HMI Command Unit
  • Coding Card

Related codes

Full explanation for 9b:1 to 9b:127
9b:70

Your boiler is notifying you that it has received a request for heat from an external source, such as a thermostat or control system, that is lower than the minimum temperature the boiler is currently programmed to provide.

Low DIY-safe £0-80

What to check first

  1. Check your external thermostat or heating controller settings to ensure the target temperature isn't set unusually low.
  2. Restart the boiler to see if the advisory code clears.
  3. No immediate action is required if your heating and hot water are currently working as expected, as this is often an advisory status code.

Parts commonly replaced

  • External controller
  • Communication module

Related codes

Full explanation for 9b:70
9C

Your boiler has lost its connection to the sensor that monitors the temperature of your hot water cylinder, meaning it cannot properly manage your hot water supply.

Medium Engineer only £90-180

Parts commonly replaced

  • NTC Cylinder Temperature Sensor
  • Sensor wiring harness

Related codes

Full explanation for 9C
9C:0

Your boiler has detected an internal communication failure related to its electronic control system, preventing it from monitoring safe operation.

High Engineer only £180-£450

Parts commonly replaced

  • Coding card
  • Electronic PCB
  • Control Unit

Related codes

Full explanation for 9C:0
9C:5 to 9C:60

Your boiler has identified a minor internal timing error, often related to the programming board or a sensor that is out of range.

High DIY-safe £100-250

What to check first

  1. Wait for the timer to count down and the code to disappear naturally
  2. Check that you haven't accidentally entered a test mode via the control panel
  3. If the code persists for over an hour, try a simple reset of the boiler

Parts commonly replaced

  • Electronic control board
  • Internal wiring harness

Related codes

Full explanation for 9C:5 to 9C:60
Showing 21–30 of 156
9C:20

Your boiler has lost communication with its external control modules or accessories, such as a remote thermostat or heat pump interface.

Medium DIY-safe £90-250

What to check first

  1. Check that any external thermostats or control panels have power and are switched on
  2. Turn the boiler power off at the main isolation switch, wait 30 seconds, and turn it back on to reset the communication bus
  3. Inspect the cables connecting your thermostat to the boiler for any obvious signs of damage

Parts commonly replaced

  • LON communication module
  • External sensor
  • Control unit PCB

Related codes

Full explanation for 9C:20
9F

Your boiler has lost communication with the solar heating system or has detected a fault within the solar control unit.

Low DIY-safe £100-350

What to check first

  1. Locate the solar control unit and check for any obvious error messages on its specific display
  2. Check if the solar pump station is plugged in and the power switch is turned on
  3. Perform a 'Soft Reset' by turning the boiler off and back on at the main fused spur

Parts commonly replaced

  • Solar control module
  • Communication cable (KM-BUS)
  • Solar temperature sensor

Related codes

Full explanation for 9F
9F:0 to 9F:40

Your boiler is notifying you that there is a specific temperature difference between the water flowing out and returning, which usually indicates an adjustment is needed in the system's settings or water flow.

Low DIY-safe £80-160

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the central heating system pressure is between 1.0 and 1.5 bar
  3. Bleed any air from radiators to ensure smooth water flow

Parts commonly replaced

  • Circulation pump
  • Temperature sensors

Related codes

Full explanation for 9F:0 to 9F:40
9F:8

Your boiler has detected that one of your heating zones is not heating up as quickly as it should compared to the main system.

Medium Engineer only £120-280

Parts commonly replaced

  • Mixing valve motor
  • Flow temperature sensor
  • Circulation pump

Related codes

Full explanation for 9F:8
10

Your boiler's outside temperature sensor has developed an electrical fault, causing the system to behave as if it is exactly 0°C outdoors regardless of the actual weather.

Low Engineer only £120-£200

Parts commonly replaced

  • Outside temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for 10
18

Your boiler has lost connection to its outdoor sensor, causing it to think it is freezing outside and potentially making your radiators warmer than necessary.

Low DIY-safe £90-180

What to check first

  1. Locate the outdoor sensor on your external wall
  2. Check for any visible damage or loose wires leading to the sensor unit
  3. Ensure the sensor is not covered by debris or snow
  4. Reset the boiler to see if the fault clears

Parts commonly replaced

  • Outdoor temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for 18
20

Your boiler has lost its connection to the temperature sensor that monitors the main water flow, likely due to a faulty electrical component or sensor.

High Engineer only £140-230

Parts commonly replaced

  • System flow temperature sensor (NTC)
  • Sensor lead/wiring harness

Related codes

Full explanation for 20
28

Your boiler has lost connection with a temperature sensor that monitors the main water flow, meaning it cannot accurately regulate how much heat to send to your radiators.

High Engineer only £120-210

Parts commonly replaced

  • System flow temperature sensor
  • Flow sensor wiring harness
  • Low loss header sensor

Related codes

Full explanation for 28
30

Your boiler has stopped working because its internal temperature gauge has failed, causing the system to lock the burner for safety.

High Engineer only £140-£220

Parts commonly replaced

  • Boiler flow temperature sensor (NTC)
  • Wiring harness

Related codes

Full explanation for 30
34:0

Your boiler is receiving a constant request for heat from an outside control, which is causing all of your heating pumps to run at the same time.

Low DIY-safe £90-180

What to check first

  1. Check your room thermostat to ensure it is not set higher than current room temperature.
  2. Verify if an external heating controller or 'Summer/Winter' switch is stuck in the 'On' position.
  3. Try restarting the boiler using the main power switch to reset the external signal communication.

Parts commonly replaced

  • External room thermostat
  • Wiring centre
  • Internal PCB (Control unit)

Related codes

Full explanation for 34:0
Showing 31–40 of 156
34:1

Your boiler is confused by an external signal telling it to run the heating pump, which may be caused by a faulty control module or a wiring problem.

Medium DIY-safe £120-350

What to check first

  1. Locate the reset button on the front control panel.
  2. Press and hold the reset button for 2 to 3 seconds.
  3. Wait for the boiler to restart; if the code returns, contact a professional to check the system configuration.

Parts commonly replaced

  • Extension module
  • Communication cable
  • Internal pump control board

Related codes

Full explanation for 34:1
34:2

Your boiler has detected an unusual communication signal from an external control or pump, meaning the system is confused about when it should be running.

Medium Engineer only £120-350

Parts commonly replaced

  • Internal circulation pump
  • Extension module
  • Wiring harness

Related codes

Full explanation for 34:2
38

Your boiler has stopped working because it can no longer accurately measure its own internal temperature due to a broken wire or faulty sensor.

High Engineer only £120-£210

Parts commonly replaced

  • Boiler temperature sensor (NTC)
  • Wiring harness

Related codes

Full explanation for 38
40

Your boiler has detected a technical fault with a sensor on one of your heating zones, which means that specific part of your heating will likely shut down to prevent damage.

Medium Engineer only £120-£220

Parts commonly replaced

  • Flow temperature NTC sensor
  • Sensor wiring harness
  • MCM (Mixer Control Module)

Related codes

Full explanation for 40
48

Your boiler has lost communication with a temperature sensor in your secondary heating zone, causing that specific circuit to shut down as a safety precaution.

Medium Engineer only £120-£210

Parts commonly replaced

  • Flow temperature sensor (NTC)
  • Connecting cable harness

Related codes

Full explanation for 48
50

Your boiler is unable to heat your water because the temperature sensor for your hot water cylinder has failed or has a wiring fault.

High Engineer only £110-190

Parts commonly replaced

  • NTC Cylinder Temperature Sensor
  • Sensor wiring harness

Related codes

Full explanation for 50
50:0

Your boiler has failed to recognize its current control screen or operating interface and is trying to switch to an alternative control method.

Medium Engineer only £120-350

Parts commonly replaced

  • HMI Operating Unit
  • Main PCB
  • Connection Cable

Related codes

Full explanation for 50:0
50:1

Your boiler has lost its connection to the outside temperature sensor, which means the system doesn't know how hard it needs to work to heat your home.

Medium Engineer only £120-220

Parts commonly replaced

  • Outdoor temperature sensor
  • Sensor wiring

Related codes

Full explanation for 50:1
50:3

Your boiler's outside temperature sensor has stopped communicating with the system, which may cause your heating to run less efficiently.

Low Engineer only £120-220

Parts commonly replaced

  • Outside temperature sensor
  • Wiring/cabling to sensor

Related codes

Full explanation for 50:3
51

Your boiler is unable to heat your hot water cylinder because it has detected a faulty or short-circuited temperature sensor.

High Engineer only £120-190

Parts commonly replaced

  • NTC Cylinder Temperature Sensor
  • Wiring harness

Related codes

Full explanation for 51
Showing 41–50 of 156
52:0

Your boiler has lost communication with a sensor that monitors water temperature moving through your heating system, which may prevent it from heating your home efficiently or at all.

High Engineer only £120-220

Parts commonly replaced

  • Low loss header flow temperature sensor (NTC)
  • Wiring harness
  • Sensor clip/pocket

Related codes

Full explanation for 52:0
52:1

Your boiler has lost communication with a sensor that monitors the water temperature in the system's mixing chamber, which can cause inefficient heating.

Medium Engineer only £120-220

Parts commonly replaced

  • Low loss header flow temperature sensor
  • NTC thermistor sensor wiring harness

Related codes

Full explanation for 52:1
53:0

Your boiler has detected an internal electrical communication error or a fault with one of its main control components, which is preventing it from running properly.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB (Control Board)
  • Function Relay Module
  • Internal Wiring Loom

Related codes

Full explanation for 53:0
53:1

Your boiler has detected a technical issue with the internal pump responsible for circulating hot water around your taps.

Medium Engineer only £140-£320

Parts commonly replaced

  • DHW Circulation Pump
  • Internal Extension Module
  • Wiring Harness

Related codes

Full explanation for 53:1
53:2

Your boiler's internal computer is reporting an electrical fault with the pump that circulates hot water to your radiators, meaning your heating may not turn on correctly.

High Engineer only £180-450

Parts commonly replaced

  • External heating circuit pump
  • Internal wiring harness
  • PCB (Control board)

Related codes

Full explanation for 53:2
53:3

Your boiler is having trouble communicating with the pump that fills your separate hot water tank, meaning your home's hot water supply may be affected.

Medium Engineer only £140-£350

Parts commonly replaced

  • Function Relay
  • Cylinder Loading Pump
  • Wiring Harness
  • Electronic Module

Related codes

Full explanation for 53:3
54:0

Your boiler is confused because it is trying to communicate with a solar heating panel system that it cannot find or that isn't connected.

Low DIY-safe £80-160

What to check first

  1. Locate the 'OK' and 'Menu' buttons (or the touchscreen menu).
  2. Navigate to the 'Service' or 'Settings' sub-menu.
  3. Restart the boiler using the main power switch to see if it clears the communication error.

Parts commonly replaced

  • Communication Module
  • Solar Control Unit PCB

Related codes

Full explanation for 54:0
54:1

Your boiler's solar control system is having trouble communicating with its temperature sensors or the pump, meaning your solar water heating may not be working correctly.

Low Engineer only £90-220

Parts commonly replaced

  • Solar temperature sensor
  • Vitosolic 100 communication cable
  • Solar pump station

Related codes

Full explanation for 54:1
54:2

Your boiler is having trouble communicating with your solar heating control system, meaning your solar panels may not be providing hot water as intended.

Low Engineer only £90-180

Parts commonly replaced

  • Communication Module
  • KM-BUS Cable
  • Vitosolic Controller

Related codes

Full explanation for 54:2
56:0

Your boiler is experiencing a communication issue with its internal hot water controls, which may limit the temperature settings available to you.

Low DIY-safe £120-250

What to check first

  1. Turn the boiler power off at the main fused spur switch
  2. Wait 60 seconds
  3. Turn the power back on and see if the code clears

Parts commonly replaced

  • DHW Temperature Sensor
  • Controller Coding Plug

Related codes

Full explanation for 56:0
Showing 51–60 of 156
56:1

Your boiler's hot water setting is incorrectly configured or a sensor is reporting a temperature outside of the normal operating range.

Low DIY-safe £0-120

What to check first

  1. Check your hot water temperature settings on the boiler control panel.
  2. Ensure the target hot water temperature is set between 40°C and 60°C.
  3. Try resetting the boiler to clear the advisory code.

Parts commonly replaced

  • DHW temperature sensor (NTC thermistor)
  • Wiring harness

Related codes

Full explanation for 56:1
58

Your boiler is unable to heat your water because the sensor that monitors your hot water cylinder temperature has lost its electrical connection.

High Engineer only £90-180

Parts commonly replaced

  • NTC Cylinder Temperature Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for 58
58:0

Your boiler is struggling to heat your hot water tank because it cannot detect or communicate with a required component or sensor.

High Engineer only £120-350

Parts commonly replaced

  • Cylinder temperature sensor
  • NTC thermistor
  • Electronic control PCB

Related codes

Full explanation for 58:0
58:1 to 58:95

Your boiler is notifying you of an incorrectly set or restricted hot water temperature limit that needs adjustment in the system settings.

Low DIY-safe £0-80

What to check first

  1. Navigate to the boiler's control panel menu
  2. Locate the hot water temperature settings
  3. Adjust the maximum set point to your desired temperature (typically 55-60°C)
  4. Refer to address 56 in your user manual if the setting remains restricted

Related codes

Full explanation for 58:1 to 58:95
59

Your boiler is unable to provide hot water because it has lost its connection to one of the sensors that monitors the temperature inside your hot water tank.

High Engineer only £120-190

Parts commonly replaced

  • Cylinder temperature sensor NTC
  • Sensor wiring harness

Related codes

Full explanation for 59
59:0

Your boiler is notifying you of a minor adjustment in how it monitors your hot water tank temperature, which shouldn't immediately stop your system from working.

Low Engineer only £90-180

Parts commonly replaced

  • DHW cylinder temperature sensor
  • Sensor wiring harness

Related codes

Full explanation for 59:0
59:1 to 59:10

Your boiler is notifying you of an adjustable temperature setting related to the DHW cylinder pump, which is usually a configuration advisory rather than a mechanical failure.

Low DIY-safe £90-180

What to check first

  1. Press the 'Reset' button on the control panel
  2. Turn the boiler off and back on at the fused spur switch
  3. Monitor the display to see if the code clears after a restart

Parts commonly replaced

  • DHW cylinder temperature sensor
  • Expansion PCB

Related codes

Full explanation for 59:1 to 59:10
60:5 to 60:25

Your boiler is struggling to reach the desired temperature for your hot water because the internal settings or parts aren't coordinating correctly.

Medium DIY-safe £120-280

What to check first

  1. Check the hot water temperature setting on the boiler control panel
  2. Try resetting the boiler to see if the communication error clears
  3. Monitor if the hot water feels significantly cooler than the set temperature

Parts commonly replaced

  • DHW temperature sensor
  • Diverter valve
  • Plate heat exchanger

Related codes

Full explanation for 60:5 to 60:25
60:10

Your boiler is getting much hotter than expected while trying to heat your water, which usually suggests the heat isn't transferring properly or a sensor is misreading.

Medium Engineer only £120-280

Parts commonly replaced

  • Plate heat exchanger
  • DHW temperature sensor
  • Diverter valve motor

Related codes

Full explanation for 60:10
62:0

Your boiler's internal pump has stopped circulating water properly after the burners turn off, which can cause the system to overheat and shut down.

High Engineer only £250-£450

Parts commonly replaced

  • Internal circulation pump
  • Pump control module
  • Main PCB

Related codes

Full explanation for 62:0
Showing 61–70 of 156
62:1 to 62:15

Your boiler is notifying you of the current pump run-on settings rather than an actual fault, essentially staying operational for a set time after central heating is turned off.

Low DIY-safe

What to check first

  1. Check the user manual to see if you wish to adjust the fan or pump run-on duration.
  2. No action is required if the boiler is providing heating and hot water as normal.
  3. Restart the boiler to clear the display if it is stuck on this status code.

Related codes

Full explanation for 62:1 to 62:15
62:2

Your boiler's internal pump is running longer than expected to cool the system down, which may indicate a minor circulation issue or a sensor communication glitch.

Low DIY-safe £0-120

What to check first

  1. Check that all radiator valves (TRVs) are open to ensure water can circulate freely.
  2. Restart the boiler using the power button to see if the message clears.
  3. Ensure the system pressure gauge is between 1.0 and 1.5 bar.

Parts commonly replaced

  • Pump speed controller
  • Internal circulation pump

Related codes

Full explanation for 62:2
63:0

Your boiler is struggling to correctly communicate with its internal control system regarding how it should heat your hot water tank.

Medium DIY-safe £100-250

What to check first

  1. Turn the boiler's power switch off for 30 seconds
  2. Switch the power back on and wait for the system to reboot
  3. Check if the hot water function operates normally

Parts commonly replaced

  • External controller module
  • Electronic control PCB
  • Wiring harness components

Related codes

Full explanation for 63:0
63:1

Your boiler is performing a routine automatic safety check and system cleaning once a day to ensure everything is working correctly.

Low DIY-safe

What to check first

  1. No action required; this is a normal operating status message rather than a breakdown.
  2. Monitor the display to ensure it returns to the standard temperature reading automatically.
  3. If the code stays on the screen permanently, try a simple reset.
Full explanation for 63:1
63:2 to 63:14

Your boiler is experiencing a communication error with the internal control system that is intermittently disrupting your heating and hot water.

Medium Engineer only £350-700

Parts commonly replaced

  • Electronic Control Unit (Main PCB)
  • Coding Card

Related codes

Full explanation for 63:2 to 63:14
63:15

Your boiler has experienced a specific internal electronic error that has occurred twice within a 24-hour period, indicating a persistent fault.

High Engineer only £350-700

Parts commonly replaced

  • PCB (Main Circuit Board)
  • Burner Control Unit

Related codes

Full explanation for 63:15
65:0

Your boiler is having trouble managing how it sends heat to your radiators or hot water cylinder because it cannot detect or communicate with a key internal control valve.

High Engineer only £180-350

Parts commonly replaced

  • Diverter valve motor
  • Wiring harness
  • Control PCB

Related codes

Full explanation for 65:0
65:1

Your boiler is struggling to direct heated water to either your radiators or your hot water taps because a motorized internal valve has become stuck or failed.

High Engineer only £180-350

Parts commonly replaced

  • Diverter valve motor
  • Diverter valve cartridge
  • Wiring harness

Related codes

Full explanation for 65:1
65:2

Your boiler is having trouble directing water to your radiators or taps because an internal motor has likely become stuck or failed.

High Engineer only £180-£320

Parts commonly replaced

  • Diverter valve motor
  • Diverter valve cartridge
  • Wilo actuator

Related codes

Full explanation for 65:2
65:3

Your boiler has detected an internal communication or performance issue with the device that switches water between your radiators and your taps.

Medium Engineer only £180-£350

Parts commonly replaced

  • Diverter valve motor
  • Grundfos actuator
  • Diverter valve cartridge

Related codes

Full explanation for 65:3
Showing 71–80 of 156
67:0 to 67:60

Your boiler is notifying you that the hot water temperature setting is currently limited or being adjusted across its standard range.

Low DIY-safe £0-80

What to check first

  1. Check the hot water temperature settings on the boiler control panel
  2. Adjust the dial or digital temperature setting to your preference
  3. Restart the boiler to clear the notification from the display

Parts commonly replaced

  • Electronic Control Unit (PCB)
  • Communication Module

Related codes

Full explanation for 67:0 to 67:60
67:40

Your boiler's solar heating accessory has detected a minor internal setting mismatch or a sensor communication issue regarding your hot water targets.

Low DIY-safe £60-120

What to check first

  1. Locate the Vitosolic solar control unit and check for any separate power switches.
  2. Perform a standard reset of the boiler's control panel by pressing the reset button.
  3. Check that the solar cylinders temperature settings have not been adjusted to an unusually high or low level.

Parts commonly replaced

  • Solar Cylinder Temperature Sensor
  • Solar Control Cable

Related codes

Full explanation for 67:40
71:0

Your boiler is notifying you that the hot water pump is running based on its set schedule, which is usually a normal operational message rather than a breakdown.

Low DIY-safe £0-80

What to check first

  1. Check your hot water time program settings on the control panel
  2. Adjust the 'DHW circulation' schedule if the pump is running at unwanted times
  3. Reset the boiler to see if the advisory code clears

Parts commonly replaced

  • None (programming adjustment)
  • DHW Circulation Pump (if noisy)

Related codes

Full explanation for 71:0
71:1

Your boiler is struggling to heat your hot water tank because it is reaching its internal safety temperature limit before the tank is actually full.

High Engineer only £150-450

Parts commonly replaced

  • Cylinder temperature sensor
  • Plate heat exchanger
  • Internal circulation pump
  • Diverter valve

Related codes

Full explanation for 71:1
71:2

Your boiler is having trouble heating your hot water cylinder effectively because it is not reaching the required temperature during the heating process.

Medium Engineer only £120-£350

Parts commonly replaced

  • Cylinder temperature sensor
  • Diverter valve
  • Plate heat exchanger

Related codes

Full explanation for 71:2
72:0

Your boiler is notifying you that your hot water circulation pump is currently running as scheduled, but it may be staying active because of a sensor communication issue.

Low DIY-safe £90-180

What to check first

  1. Check your hot water time program settings on the control panel
  2. Switch the boiler off and back on to refresh the system communication
  3. Monitor for any changes in hot water temperature or delivery speed

Parts commonly replaced

  • Cylinder temperature sensor
  • Internal wiring harness
  • DHW circulation pump

Related codes

Full explanation for 72:0
72:1

Your boiler is struggling to accurately measure the temperature of the water being heated for your taps, causing it to shut down while filling your hot water cylinder.

Medium Engineer only £140-£260

Parts commonly replaced

  • Cylinder temperature sensor
  • Sensor wiring harness
  • NTC thermistor

Related codes

Full explanation for 72:1
72:2

Your boiler has detected that a hot water sensor is reporting a temperature increase when it was not expected to, likely due to a sensor being in the wrong position or failing.

Low Engineer only £90-180

Parts commonly replaced

  • Cylinder temperature sensor
  • NTC thermistor
  • Wiring harness

Related codes

Full explanation for 72:2
73:0

Your boiler's hot water pump is scheduled to be running, but it may not be operating correctly or is being flagged for an advisory check.

Low DIY-safe £90-180

What to check first

  1. Check your hot water time program settings on the control panel
  2. Ensure the pump is not physically stuck or blocked
  3. Reset the boiler to see if the advisory code clears

Parts commonly replaced

  • DHW Circulation Pump
  • Pump Cable/Connector

Related codes

Full explanation for 73:0
73:1 to 73:6

Your boiler's hot water heating pump or valve is turning on and off more frequently than planned due to a possible configuration or sensing issue.

Low DIY-safe £90-180

What to check first

  1. This is often a status notification rather than a breakdown.
  2. Check your hot water time program settings on the control panel.
  3. Ensure your legionella protection or DHW circulation pump settings match your daily needs.

Parts commonly replaced

  • Cylinder temperature sensor
  • Diverter valve motor
  • Control PCB

Related codes

Full explanation for 73:1 to 73:6
Showing 81–90 of 156
73:7

Your boiler has detected a communication error with its internal control system or a connected smart module, which may prevent it from managing your heating correctly.

Medium Engineer only £120-350

Parts commonly replaced

  • Communication module
  • Electronic control PCB
  • Wiring harness

Related codes

Full explanation for 73:7
76:0

Your boiler's internal communication system has stopped talking to a network expansion module, which may affect how advanced heating zones or external controls are managed.

Medium Engineer only £120-350

Parts commonly replaced

  • LON communication module
  • Control PCB
  • Data cables

Related codes

Full explanation for 76:0
76:1

Your boiler is having trouble communicating with its internal network or external control accessories.

Medium DIY-safe £120-350

What to check first

  1. Turn the boiler power off at the main isolation switch.
  2. Wait for 30 seconds.
  3. Turn the power back on to see if the system resets and recognises the module.

Parts commonly replaced

  • LON communication module
  • Internal wiring harness
  • Heat manager PCB

Related codes

Full explanation for 76:1
76:2

Your boiler is having difficulty communicating with its internal electronics or the module that controls multiple heating zones.

Medium Engineer only £120-350

Parts commonly replaced

  • KM-BUS communication module
  • Control circuit board
  • Wiring harness

Related codes

Full explanation for 76:2
77:1

Your boiler's internal communication system has detected two components trying to use the same identification number, causing a minor configuration conflict.

Low DIY-safe £80-120

What to check first

  1. Navigate to the boiler control panel menu.
  2. Perform a system reset to see if the communication error clears automatically.
  3. If you have recently added a new remote control or smart module, check the manual for how to assign a unique participant number.

Parts commonly replaced

  • LON communication module
  • Extension PCB
Full explanation for 77:1
77:2 to 77:99

Your boiler is having difficulty communicating with other smart controls or connected devices on your home heating network.

Low DIY-safe £0-120

What to check first

  1. Locate the power switch for your boiler and any external heating controllers.
  2. Turn the power off at the fused spur for 30 seconds, then turn it back on to restart the communication network.
  3. Check that any internet-connected modules or smart thermostats (like Vitocom) have a stable power supply and connection.

Parts commonly replaced

  • LON communication module
  • Vitocom gateway
  • Network cable

Related codes

Full explanation for 77:2 to 77:99
79:0

Your boiler's internal computer system has lost its configuration settings and no longer knows how to coordinate the heating system.

High DIY-safe £120-450

What to check first

  1. Locate the main power switch for the boiler and turn it off.
  2. Wait for approximately 60 seconds.
  3. Turn the power back on and press the 'Reset' button on the front control panel.

Parts commonly replaced

  • Main PCB (Control Unit)
  • Coding Chip

Related codes

Full explanation for 79:0
79:1

Your boiler's electronic brains are experiencing a communication conflict or an internal memory error, which may cause the system to stop working correctly.

Medium DIY-safe £120-450

What to check first

  1. Locate the power switch or fused spur for the boiler
  2. Turn the power off for 30 seconds
  3. Turn the power back on and wait for the system to reboot

Parts commonly replaced

  • LGM18 Control Board
  • EBC 02 Electronic Module

Related codes

Full explanation for 79:1
80:0

Your boiler has detected a communication error with its internal control system or a connected sensor, which might cause it to operate incorrectly or stop working.

Medium DIY-safe £120-350

What to check first

  1. Turn the boiler power switch off
  2. Wait for 60 seconds
  3. Turn the boiler back on to see if the fault clears

Parts commonly replaced

  • External temperature sensor
  • Internal wiring harness
  • Control PCB

Related codes

Full explanation for 80:0
80:1

Your boiler has detected a persistent communication issue with its external sensors or internal control system that has lasted more than five seconds.

Medium DIY-safe £120-280

What to check first

  1. Navigate to the boiler control panel
  2. Perform a system reset by pressing the RESET button
  3. Check for any loose external wiring if visible and safe to touch

Parts commonly replaced

  • Outdoor temperature sensor
  • Communication cable
  • Internal control PCB

Related codes

Full explanation for 80:1
Showing 91–100 of 156
80:2 to 80:199

Your boiler is waiting for a pre-set delay period to pass before restarting, often caused by a temporary communication gap or a signal issue between internal components.

Low DIY-safe £0-120

What to check first

  1. Wait for 15-20 minutes to see if the delay timer expires and the boiler restarts automatically.
  2. Perform a standard reset by pressing the 'Reset' button or turning the power off and on once.
  3. Check if the room thermostat or external controls are calling for heat.

Parts commonly replaced

  • No parts usually required
  • Bus communication cable
  • Control PCB

Related codes

Full explanation for 80:2 to 80:199
81:0

Your boiler has been manually switched between heating and hot water modes, and it is simply notifying you that a changeover has occurred.

Low DIY-safe

What to check first

  1. Check the control panel to see if Summer or Winter mode was selected recently
  2. Navigate the menu to 'Heating and Hot Water' settings
  3. Adjust the date and time settings to ensure the automatic changeover works correctly in the future

Related codes

Full explanation for 81:0
81:1

Your boiler is notifying you that it has automatically switched between heating and hot water mode based on the outside temperature.

Low DIY-safe

What to check first

  1. Check the outside temperature sensor is not covered or obstructed
  2. Adjust the summer/winter threshold temperature in the user settings if the house feels too cold
  3. Monitor the boiler to ensure it switches back when the temperature drops

Related codes

Full explanation for 81:1
81:2

Your boiler is notifying you that it has detected and is automatically setting up its wireless clock module.

Low DIY-safe £0-120

What to check first

  1. Wait for the boiler to finish its automatic synchronisation process
  2. Monitor the display to ensure the code clears and the time updates correctly
  3. Restart the boiler once if the code persists for more than 30 minutes

Parts commonly replaced

  • Radio clock receiver module
  • Communication cable

Related codes

Full explanation for 81:2
81:3

Your boiler is having trouble synchronizing its internal clock with an external control system, which might affect your heating schedules.

Low DIY-safe £0-120

What to check first

  1. Locate the main control panel and manually set the time and date.
  2. Restart the boiler system to re-establish the communication link.
  3. Check if any external thermostats or smart controls have lost power or connection.

Parts commonly replaced

  • LON communication module
  • External sensor battery

Related codes

Full explanation for 81:3
88:0

Your boiler is confirming it is set to show temperatures in Celsius, which is a normal setting rather than a breakdown.

Low DIY-safe

What to check first

  1. Navigate to the main display menu
  2. Acknowledge the notification by pressing 'OK' or the return arrow
  3. Rest the boiler if the display remains stuck on this status screen

Related codes

Full explanation for 88:0
88:1

Your boiler's control panel has switched from Celsius to Fahrenheit, meaning temperatures are being displayed using a different measurement system rather than showing a mechanical fault.

Low DIY-safe

What to check first

  1. Navigate to the boiler's settings menu using the control dial or touch interface.
  2. Look for the 'Display' or 'Configuration' sub-menu.
  3. Locate the temperature unit setting and change it back from '°F' to '°C'.
Full explanation for 88:1
90:0 to 90:199

Your boiler's control system is struggling to adjust the internal water temperature correctly in response to changes in the weather outside.

Low Engineer only £100-£250

Parts commonly replaced

  • Outside temperature sensor
  • Control PCB
  • Wiring harness

Related codes

Full explanation for 90:0 to 90:199
90:128

Your boiler's outside temperature sensor has failed or is giving an incorrect reading, meaning the system may not heat your home efficiently based on the weather.

Low Engineer only £120-220

Parts commonly replaced

  • Outside temperature sensor
  • Sensor wiring lead

Related codes

Full explanation for 90:128
91:0

Your boiler is having trouble communicating with an external control device, meaning some advanced settings or remote switching may not work as expected.

Low DIY-safe £0-120

What to check first

  1. Check that any external thermostats or control hubs are powered on
  2. Ensure your home Wi-Fi or internet connection is stable if using smart controls
  3. Reset the boiler to see if the communication link restores itself

Parts commonly replaced

  • External extension module
  • Communication cable
  • Smart thermostat gateway

Related codes

Full explanation for 91:0
Showing 101–110 of 156
91:1

Your boiler is receiving a request to change its heating schedule from an external source, but it cannot apply this to your specific heating setup.

Low DIY-safe £0-90

What to check first

  1. Check if any external smart thermostats or controllers have conflicting schedules
  2. Press the 'Reset' button on the control panel to clear the temporary communication error
  3. Ensure any external remote control apps are up to date

Parts commonly replaced

  • External controller
  • Communication module

Related codes

Full explanation for 91:1
91:2

Your boiler is receiving a conflicting signal from an external controller or smart thermostat that is trying to change how your heating is running.

Low DIY-safe £0-120

What to check first

  1. Check your external thermostat or wall controllers for any unusual settings or schedules
  2. Turn the boiler off and back on at the fused spur switch to reset the communication link
  3. Verify that any smart home apps connected to the heating are not sending constant override commands

Parts commonly replaced

  • External controller
  • Wiring harness

Related codes

Full explanation for 91:2
91:3

Your boiler is receiving conflicting signals about how to heat your home because an external controller is trying to switch settings for several heating zones at once.

Low DIY-safe £0-120

What to check first

  1. Check any external smart thermostats or zone controllers for low batteries or error messages
  2. Ensure all external timers and programmers are set to the same heating mode
  3. Perform a simple reset of the boiler using the power button to clear the communication glitch

Parts commonly replaced

  • External programmer unit
  • Wiring harness
  • Communication module

Related codes

Full explanation for 91:3
92

Your boiler has detected a fault with the sensor that monitors the temperature of your solar panels, meaning the solar heating system will not work correctly.

Low Engineer only £120-£210

Parts commonly replaced

  • Solar collector temperature sensor
  • Sensor wiring harness

Related codes

Full explanation for 92
93

Your boiler has detected a technical fault with a sensor in your solar heating system, which means your solar panels may not be contributing to your hot water as they should.

Low Engineer only £90-180

Parts commonly replaced

  • Solar cylinder temperature sensor
  • Sensor wiring harness
  • Solar control module

Related codes

Full explanation for 93
94

Your boiler has detected a fault with the sensor that monitors the temperature of your solar hot water tank, meaning your solar thermal system may not heat your water correctly.

Low Engineer only £120-£190

Parts commonly replaced

  • Solar cylinder temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for 94
95:0

Your boiler has lost its connection to its remote communication module, meaning you cannot control your heating via the app, but your hot water and heating should still work manually.

Low DIY-safe £0-90

What to check first

  1. Check that your internet router is switched on and working
  2. Ensure the Vitocom 100 module is plugged in and has power
  3. Identify if the communication cable between the boiler and the module has become loose

Parts commonly replaced

  • Vitocom 100 communication module
  • Communication cable (plug-in)

Related codes

Full explanation for 95:0
95:1

Your boiler is having trouble communicating with the external internet or remote control monitoring accessory.

Low DIY-safe £60-120

What to check first

  1. Check that your internet router is switched on and working
  2. Ensure all cables between the boiler and the communication module are securely plugged in
  3. Reset the boiler to see if the communication link restarts

Parts commonly replaced

  • Vitocom 100 interface module
  • Communication cable pack

Related codes

Full explanation for 95:1
97:0

Your boiler is notifying you that it is using the reading from the outdoor temperature sensor to manage its operation, which may be a temporary update or a minor communication check.

Low DIY-safe £0-120

What to check first

  1. Check the outdoor sensor is not covered by snow, ice, or debris
  2. Monitor the boiler display to see if the message clears automatically
  3. Restart the boiler once to see if the advisory code clears

Parts commonly replaced

  • Outdoor temperature sensor
  • Sensor wiring/cabling

Related codes

Full explanation for 97:0
97:1

Your boiler is receiving the outside temperature reading from a separate networking component rather than its own dedicated sensor.

Low DIY-safe £0-80

What to check first

  1. Locate the fault code on the display
  2. Press the 'OK' or 'Reset' button to acknowledge the notification
  3. Monitor the display to see if the message reappears or if heating performance changes

Parts commonly replaced

  • None (Software configuration)
  • LON communication module

Related codes

Full explanation for 97:1
Showing 111–120 of 156
97:2

Your boiler is having difficulty communicating with part of your heating control system, but it will continue to work using its own internal information.

Low DIY-safe £60-120

What to check first

  1. Check for any visible damage to wiring leading to the outdoor sensor
  2. Switch the boiler off and back on at the fused spur to refresh the connection
  3. If you have a Vitotronic 050 controller, check that it is powered on

Parts commonly replaced

  • LON communication module
  • External temperature sensor
  • Wiring harness

Related codes

Full explanation for 97:2
98:1

Your boiler is having difficulty communicating with the external system that monitors several heating units at once.

Low DIY-safe £0-120

What to check first

  1. Check that your internet router and hub are plugged in and switched on
  2. Identify if any other system monitors or Vitocom devices have lost power
  3. Press the 'Reset' button on the boiler control panel once

Parts commonly replaced

  • Vitocom 300 communication module
  • Connecting cables
  • External gateway

Related codes

Full explanation for 98:1
98:1 to 98:5

Your boiler has detected an internal configuration error or a communication fault with its electronic control system.

High Engineer only £180-450

Parts commonly replaced

  • Electronic Control Unit (PCB)
  • Communication module

Related codes

Full explanation for 98:1 to 98:5
A0:0

Your boiler has lost communication with its remote control or thermostat, meaning it cannot receive temperature instructions.

Medium DIY-safe £0-120

What to check first

  1. Check batteries in your wireless room thermostat or remote control
  2. Ensure the wireless receiver plugged into the boiler is powered on
  3. Restart your home internet router if your heating uses a smart app control

Parts commonly replaced

  • Thermostat batteries
  • Remote control transmitter
  • Communication module

Related codes

Full explanation for A0:0
A0:1

Your boiler has lost communication with its remote control unit, meaning it may not be receiving the correct instructions to heat your home.

Medium DIY-safe £90-250

What to check first

  1. Check the thermostat or remote control unit is properly docked/mounted
  2. Inspect the wiring between the boiler and the wall controller for any obvious loose connections
  3. Turn the boiler power off and back on to trigger a re-recognition of the remote unit

Parts commonly replaced

  • Vitotrol 200 Remote Control unit
  • Communication cable
  • Internal boiler PCB

Related codes

Full explanation for A0:1
A0:2

Your boiler has lost communication with your wall-mounted remote control unit, meaning the thermostat cannot talk to the boiler to manage your heating.

Medium DIY-safe £90-250

What to check first

  1. Check that the Vitotrol unit is fully clipped into its wall base
  2. Inspect the wiring between the control and the boiler for any obvious loose connections if accessible
  3. Turn the boiler power off and back on at the fused spur to attempt a communication reset

Parts commonly replaced

  • Vitotrol 300 Remote Control
  • KM-Bus communication module

Related codes

Full explanation for A0:2
A2:0

Your boiler is struggling to prioritise between heating your home and heating your hot water because it has detected a pump or valve communication issue.

Medium Engineer only £120-280

Parts commonly replaced

  • 3-way diverter valve
  • Heating circuit pump
  • Internal wiring harness

Related codes

Full explanation for A2:0
A2:1

Your boiler is temporarily prioritizing the heating of your hot water over your radiators, meaning your heating may feel cool for a short period while the water tank refills.

Low DIY-safe

What to check first

  1. Wait up to 30 minutes for the hot water cylinder to reach its target temperature
  2. Check if the hot water demand setting on your control panel is set unusually high
  3. Monitor the radiators to see if they begin to heat up once the hot water light goes off

Related codes

Full explanation for A2:1
A2:2

Your boiler is struggling to switch between heating your radiators and your hot water tank, meaning one of them may not be getting warm enough.

Medium Engineer only £180-350

Parts commonly replaced

  • Circulation pump
  • Diverter valve actuator
  • Mixer motor

Related codes

Full explanation for A2:2
A3:-9 to A3:15

Your boiler is automatically managing its internal pump to protect the system from freezing based on the outdoor temperature.

Low DIY-safe

What to check first

  1. Check that your outdoor temperature sensor is not covered by snow or debris
  2. Monitor the boiler display to see if the message clears as the weather warms up
  3. No action is required as this is an automated safety function

Parts commonly replaced

  • None (Normal operation)
Full explanation for A3:-9 to A3:15
Showing 121–130 of 156
A7

Your boiler's control panel has lost communication with the internal computer, making it difficult or impossible to adjust your heating settings.

Medium Engineer only £180-£450

Parts commonly replaced

  • HMI Operator Unit
  • Control Cable
  • Main PCB

Related codes

Full explanation for A7
b0

Your boiler has stopped working because it has detected an electrical fault with the sensor that monitors the safety of your exhaust gases.

High Engineer only £140-£260

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness

Related codes

Full explanation for b0
b1

Your boiler's main control panel is having trouble talking to the internal computer, meaning you cannot adjust settings or operate the unit correctly.

High Engineer only £180-450

Parts commonly replaced

  • Programming Unit
  • Control Base Module
  • Ribbon Cable

Related codes

Full explanation for b1
b4

Your boiler has encountered an internal electronic error while trying to process sensor data, which is preventing it from running properly.

High Engineer only £350-£650

Parts commonly replaced

  • Main PCB (Control Circuit Board)

Related codes

Full explanation for b4
b5

Your boiler has experienced an internal communication error or software glitch within its main electronic control unit.

High DIY-safe £350-650

What to check first

  1. Locate the power switch or fused spur for the boiler
  2. Turn the power off for 60 seconds
  3. Turn the power back on and see if the code clears

Parts commonly replaced

  • Main PCB (Control Board)
  • Coding Card

Related codes

Full explanation for b5
b7

Your boiler's internal computer chip is either missing, faulty, or not communicating correctly with the main controls, meaning the unit cannot start for safety reasons.

High Engineer only £180-450

Parts commonly replaced

  • Boiler coding card
  • Main PCB (Printed Circuit Board)

Related codes

Full explanation for b7
b8

Your boiler has stopped working because it can no longer safely monitor the temperature of the exhaust gases leaving the system.

High Engineer only £140-£220

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness connector

Related codes

Full explanation for b8
bA

Your boiler has lost communication with the control box that manages your second heating zone, meaning your underfloor heating or additional radiators may not warm up correctly.

Medium Engineer only £180-350

Parts commonly replaced

  • Mixer extension kit
  • KM-BUS connection cable
  • Electronic controller PCB

Related codes

Full explanation for bA
bC

Your boiler has lost its connection with the remote control thermostat for your main heating circuit, meaning it cannot receive instructions on when to turn the heating on.

Medium DIY-safe £90-280

What to check first

  1. Check if the batteries in your Vitotrol remote control unit need replacing.
  2. Ensure the remote control is properly docked on its wall bracket or base station.
  3. Restart the boiler using the power switch to try and refresh the communication link.

Parts commonly replaced

  • Batteries
  • Vitotrol Remote Control unit
  • Communication cable or wireless receiver

Related codes

Full explanation for bC
bd

Your boiler has lost communication with the remote control unit that manages your second heating circuit, meaning that part of your home may not heat correctly.

Medium DIY-safe £90-280

What to check first

  1. Check that the Vitotrol remote control is securely docked in its wall bracket
  2. Inspect the remote control for any low battery warnings if applicable
  3. Turn the boiler power off and back on at the fused spur switch to reset the connection

Parts commonly replaced

  • Vitotrol 200/300 Remote Control unit
  • KM-Bus communication module
  • Low voltage wiring

Related codes

Full explanation for bd
Showing 131–140 of 156
bE

Your boiler is having trouble communicating with your wall-mounted room thermostat because the settings weren't configured correctly during installation or after a power cut.

Medium Engineer only £90-160

Parts commonly replaced

  • Vitotrol remote control
  • Coding plug

Related codes

Full explanation for bE
bF

Your boiler's internal communication component is either missing, faulty, or not recognised by the main control system.

High Engineer only £180-450

Parts commonly replaced

  • LON communication module
  • Boiler control PCB

Related codes

Full explanation for bF
C2

Your boiler is having trouble talking to the solar heating system, meaning your solar panels may not be contributing to your hot water as they should.

Low DIY-safe £90-250

What to check first

  1. Check if the power switch for the solar control station is turned on
  2. Inspect the visible connection cable between the boiler and the solar unit for obvious loose plugs
  3. Reset the boiler to see if the communication link restores itself

Parts commonly replaced

  • Communication cable (KM-BUS)
  • Solar control module (SM1 or Vitosolic)
  • Boiler electronic PCB

Related codes

Full explanation for C2
C5

Your boiler is struggling to communicate with its internal pump, which means it cannot properly move heated water around your system.

High Engineer only £280-550

Parts commonly replaced

  • Internal variable speed pump
  • Pump communication cable
  • Main PCB

Related codes

Full explanation for C5
C6

Your boiler is having trouble communicating with the internal pump that moves water around your second heating zone, which may prevent some of your radiators from getting hot.

Medium Engineer only £180-450

Parts commonly replaced

  • Circulation pump
  • Internal wiring harness
  • Electronic control PCB

Related codes

Full explanation for C6
C7

Your boiler is having trouble communicating with the internal pump that moves water around your radiators, meaning your heating may not work correctly.

High Engineer only £250-£450

Parts commonly replaced

  • Internal circulation pump
  • Wiring harness
  • Control PCB

Related codes

Full explanation for C7
Cd

Your boiler has lost its connection with the remote control or internet communication module, which may stop you from controlling your heating via an app or external thermostat.

Medium DIY-safe £90-280

What to check first

  1. Locate the Vitocom 100 communication module near the boiler
  2. Check that the communication cable (KM-BUS) is securely plugged into the module
  3. Turn the boiler power off at the main fused spur, wait 30 seconds, and turn it back on to reset the connection

Parts commonly replaced

  • KM-BUS Connection Cable
  • Vitocom 100 LAN/WiFi Module
  • Internal Communication Interface

Related codes

Full explanation for Cd
CE

Your boiler is having trouble 'talking' to an external accessory, such as an extra heating controller or a smart home module.

Medium DIY-safe £90-250

What to check first

  1. Locate the external control module or thermostat receiver
  2. Check for any loose cables or plugs connecting external components to the boiler
  3. Turn the boiler power off and back on to attempt to reset the communication link

Parts commonly replaced

  • Extension module (Lon/KM-Bus)
  • Wiring harness
  • External sensor

Related codes

Full explanation for CE
CF

Your boiler's internal communication system has failed, meaning the main control board cannot talk to its connected expansion modules.

Medium Engineer only £150-450

Parts commonly replaced

  • LON communication module
  • LON connecting cable
  • Main PCB

Related codes

Full explanation for CF
dA

Your boiler has lost its connection to the indoor temperature sensor for your main heating zone, meaning it cannot accurately judge how warm your home is.

Medium Engineer only £90-180

Parts commonly replaced

  • Room temperature sensor
  • NTC thermistor
  • Wiring harness

Related codes

Full explanation for dA
Showing 141–150 of 156
db

Your boiler has lost signal from the temperature sensor that controls your second heating zone, meaning it cannot correctly regulate the warmth in that specific part of your home.

Medium Engineer only £100-190

Parts commonly replaced

  • Room temperature sensor (NTC)
  • Sensor wiring harness

Related codes

Full explanation for db
dE

Your boiler has lost connection with the sensor that monitors the temperature for your second heating zone, meaning it cannot accurately heat that specific area of your home.

Medium Engineer only £100-£220

Parts commonly replaced

  • Room temperature sensor (NTC)
  • Sensor wiring harness
  • Extension module
Full explanation for dE
E4

Your boiler has detected an issue with its incoming electrical power supply, meaning it isn't getting the steady voltage it needs to operate safely.

High Engineer only £150-500

Parts commonly replaced

  • Main PCB (Control Board)
  • External Power Supply Unit

Related codes

Full explanation for E4
E5

Your boiler is struggling to detect a flame correctly, causing it to shut down for safety purposes.

High Engineer only £120-£280

Parts commonly replaced

  • Ionisation electrode
  • Ignition lead
  • Combustion controller

Related codes

Full explanation for E5
E6

Your boiler's fan is failing to communicate correctly with the central control board, preventing the system from starting up for your safety.

High Engineer only £250-£550

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Electronic control PCB
Full explanation for E6
F0

Your boiler's main internal computer has developed a serious electronic failure and can no longer communicate with the rest of the system.

High Engineer only £450-£700

Parts commonly replaced

  • Electronic Control Unit (PCB)
  • Coding plug

Related codes

Full explanation for F0
F1

Your boiler has automatically shut down because its exhaust gases have reached an unsafely high temperature, which is often caused by a blockage or a lack of water circulation.

High Engineer only £120-350

Parts commonly replaced

  • Heat exchanger (cleaning or replacement)
  • Flue gas temperature sensor
  • Main pump
  • Flue gas limiter

Related codes

Full explanation for F1
F2

Your boiler has switched itself off because it has reached a dangerous temperature and triggered a safety cut-out to prevent overheating.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open to allow water to flow.
  2. Verify that the boiler pressure is between 1.0 and 1.5 bar on the gauge.
  3. Press the 'Reset' button on the control panel once the boiler has cooled down.

Parts commonly replaced

  • Central heating pump
  • Overheat thermostat (Limit probe)
  • Diverter valve

Related codes

Full explanation for F2
F3

Your boiler detects a flame before it has even started the ignition process, which is a safety conflict that prevents it from firing up.

High Engineer only £120-£350

Parts commonly replaced

  • Ionisation electrode
  • Ignition cable
  • Burner control unit (PCB)

Related codes

Full explanation for F3
F4

Your boiler is failing to light the flame properly, meaning it cannot provide heating or hot water for your home.

High Engineer only £120-350

Parts commonly replaced

  • Ignition electrodes
  • Ionisation lead
  • Gas valve
  • Ignition transformer

Related codes

Full explanation for F4
Showing 151–156 of 156
F7

Your boiler has detected a problem with internal pressure readings, which means it cannot safely confirm the correct flow of air for combustion.

High Engineer only £160-£300

Parts commonly replaced

  • Differential pressure sensor
  • Sensor connecting pipes
  • Main PCB

Related codes

Full explanation for F7
F8

Your boiler has detected that the fuel supply is not shutting off as quickly as it should, causing it to shut down for safety.

Emergency Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Ionisation electrode
  • Control PCB

Related codes

Full explanation for F8
F9

Your boiler is failing to start because the internal fan is not spinning at the correct speed to safely clear the exhaust gases.

High Engineer only £250-£550

Parts commonly replaced

  • Extraction fan unit
  • Electronic control PCB
  • Fan wiring harness

Related codes

Full explanation for F9
FA

Your boiler has detected that the fan is spinning faster than it should during the start-up sequence, preventing the burner from lighting safely.

High Engineer only £250-£550

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for FA
Fd

Your boiler's internal computer has detected a fault with the control system that manages the burner, preventing it from heating your home or water.

High Engineer only £350-650

Parts commonly replaced

  • Burner Control Unit
  • Ignition Transformer
  • Printed Circuit Board (PCB)

Related codes

Full explanation for Fd
FE

Your boiler's electronic control system is experiencing electrical interference or a hardware internal communication error, preventing it from operating.

High Engineer only £350-650

Parts commonly replaced

  • Main PCB (Control Board)
  • Boiler Coding Card
  • Ignition Transformer

Related codes

Full explanation for FE