Baxi Assure System Fault codes & diagnostics

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

System Natural Gas 2020-present
GC Numbers 41-470-9941-884-0141-470-8541-470-8641-470-8841-470-9341-470-8041-470-8141-470-8241-470-8341-470-84
Download the Baxi Assure System manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 51 High 8 Medium 6 Low

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
41-470-99 818 SYSTEM 2 2023–present
41-884-01 615 SYSTEM 2 2023–present
41-470-85 ASSURE 12 SYSTEM 2020–present
41-470-86 ASSURE 15 SYSTEM 2020–present
41-470-88 ASSURE 24 SYSTEM 2020–present
41-470-93 ASSURE 24 SYSTEM LPG 2020–present
41-470-80 ASSURE 13 HEAT 2020–present
41-470-81 ASSURE 16 HEAT 2020–present
41-470-82 ASSURE 19 HEAT 2020–present
41-470-83 ASSURE 25 HEAT 2020–present
41-470-84 ASSURE 30 HEAT 2020–present

All 66 documented codes

Tap any card for details

10

Your boiler has detected that the water inside the unit is getting too hot and has automatically shut itself off to prevent any damage.

High Engineer only £120-250

Parts commonly replaced

  • Pump
  • Flow sensor
  • Heat exchanger
  • System filter
12

Your boiler is attempting to light but cannot maintain a stable flame to keep itself running.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe
13

Your boiler has detected that the solar water heating panel is currently too hot and has temporarily shut itself off to prevent damage.

Low Engineer only £100-200

Parts commonly replaced

  • Solar temperature sensor
  • Solar pump
  • Solar fluid
A.00.28

Your boiler is having trouble communicating with the solar heat hardware connected to it, so it cannot currently monitor your solar energy output.

Low Engineer only £120-200

Parts commonly replaced

  • Solar temperature sensor
  • Wiring harness
A.00.29

Your boiler has detected an error with the temperature sensor connected to your solar heating system, which may prevent it from correctly reading your water temperature.

Low Engineer only £120-220

Parts commonly replaced

  • Solar temperature sensor
  • Wiring harness
A.00.34

Your boiler has lost its connection to an external temperature sensor, which means it cannot automatically adjust your heating based on the weather outside.

Low Engineer only £120-200

Parts commonly replaced

  • Outdoor temperature sensor
  • Wiring harness
A.02.06

Your boiler has stopped working because the water pressure inside your heating system has dropped too low to function safely.

High DIY-safe £0-£120

What to check first

  1. Locate the filling loop (a silver braided hose) underneath the boiler.
  2. Open the valves on both ends of the loop to allow water into the system.
  3. Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (usually 1.0 to 1.5 bar).
  4. Close both valves tightly and ensure the pressure remains stable.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Expansion vessel
A.02.18

Your boiler's computer is having trouble communicating with its internal sensors, which has caused it to stop heating your home as a safety precaution.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
A.02.36

Your boiler has lost communication with one of its internal electrical components, meaning it cannot safely operate until the connection is restored.

High Engineer only £120-250

Parts commonly replaced

  • Main PCB
  • Wiring harness
  • Pressure sensor
A.02.37

Your boiler has lost its connection to an essential internal sensor, which means it has safely shut itself down to prevent it from operating incorrectly.

High Engineer only £120-250

Parts commonly replaced

  • Wiring harness
  • PCB
  • External sensor
Showing 11–20 of 66
A.02.45

Your boiler is having trouble communicating with its internal control system, which has caused it to stop working to avoid any potential errors.

High Engineer only £150-300

Parts commonly replaced

  • PCB (Printed Circuit Board)
  • Wiring harness
A.02.46

Your boiler has detected a communication conflict between its internal controls, meaning it has temporarily stopped working to protect itself from an incorrect operating instruction.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • External controls interface
A.02.48

Your boiler has lost its specific operating instructions and cannot safely determine how to run your heating and hot water system.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
A.02.49

Your boiler's internal computer system is having trouble starting up correctly and cannot communicate with its internal components.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
A.02.54

Your boiler is having a communication breakdown with its internal control system, which means it cannot receive instructions to heat your home or water.

High Engineer only £150-300

Parts commonly replaced

  • Printed circuit board (PCB)
  • Wiring harness
A.02.55

Your boiler has lost its digital identification data, which is preventing it from starting up correctly.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
A.02.76

Your boiler has encountered a technical data error that prevents it from saving further custom settings, but it should otherwise remain operational.

Low Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
E.00 .04

Your boiler has lost its connection to the heat sensor that monitors the water returning to the system, causing it to stop working for safety reasons.

High Engineer only £120-220

Parts commonly replaced

  • Return NTC sensor
  • Wiring harness

Related codes

E.00 .05

Your boiler has stopped working because it is unable to accurately measure the temperature of the water returning to it, likely due to a loose wire or a faulty sensor.

High Engineer only £120-200

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness

Related codes

E.00 .16

Your boiler has lost the connection to the temperature sensor in your hot water cylinder, meaning it cannot tell how hot your stored water is.

Medium Engineer only £120-220

Parts commonly replaced

  • DHW sensor
  • Sensor wiring loom

Related codes

Showing 21–30 of 66
E.00 .17

Your boiler has lost the ability to accurately measure the temperature of your hot water cylinder because of a faulty connection or sensor.

Medium Engineer only £120-200
E.00 .20

Your boiler has stopped working because it cannot properly read the temperature of the exhaust fumes, making it safer to shut down than risk running incorrectly.

High Engineer only £120-220

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness

Related codes

E.00 .21

Your boiler has detected a faulty reading from its internal safety sensor and has shut down to prevent the system from getting too hot.

High Engineer only £150-250

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness
E.01 .04

Your boiler has repeatedly failed to keep its flame lit, so it has safely shut itself down to prevent any issues.

High Engineer only £120-£250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe
E.01 .12

Your boiler has detected that the water flowing back into it is hotter than the water flowing out, which confuses the system and causes it to shut down for safety.

High Engineer only £120-250

Parts commonly replaced

  • Flow NTC sensor
  • Return NTC sensor
  • Wiring harness
E.01 .17

Your boiler is struggling to push water around your heating system, which is causing it to shut down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • Flow and return temperature sensors
  • Diverter valve
E.01 .20

Your boiler has detected that it is running much hotter than it should be because something inside is blocking the heat from escaping properly.

High Engineer only £150-350

Parts commonly replaced

  • Primary heat exchanger
  • Flue sensors
  • Condensate trap
E.02 .13

Your boiler has stopped working because it has detected an issue with a safety device or a configuration setting, meaning it is preventing itself from igniting.

High Engineer only £120-250

Parts commonly replaced

  • External safety switches
  • PCB
  • Wiring loom
E.02 .17

Your boiler has lost the ability to send electronic signals to its internal gas control system, meaning it cannot safely start up or maintain heat.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Wiring harness
E.02 .35

Your boiler has lost its connection to its internal safety components, causing it to shut down to prevent unsafe operation.

High Engineer only £150-300

Parts commonly replaced

  • PCB
  • Wiring harness
  • Safety sensor
Showing 31–40 of 66
E.02 .39

Your boiler has detected that the water pressure in your heating system is too low and it has been unable to top itself up automatically.

High Engineer only £120-250

Parts commonly replaced

  • Automatic filling link
  • Pressure sensor
  • Filling loop
E.02 .47

Your boiler is having trouble communicating with an external control, such as your thermostat or programmer, preventing it from knowing when to turn the heating on.

Medium Engineer only £120-220

Parts commonly replaced

  • External thermostat
  • Wiring harness
  • PCB
E.04 .01

Your boiler has detected an electrical fault with its internal temperature monitoring system, causing it to shut down for safety.

High Engineer only £120-220

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

E.04 .02

Your boiler has lost the signal from the sensor that monitors how hot the water is inside it, so it has shut down as a precaution to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • Flow temperature sensor
  • Wiring harness

Related codes

E.04 .08

Your boiler has detected that the water inside the system has become dangerously hot and has shut itself down to prevent damage or overheating.

High Engineer only £150-300

Parts commonly replaced

  • NTC Sensor
  • Primary Heat Exchanger
  • Pump
  • Main PCB
E.04 .12

Your boiler is trying to start but the flame is not catching or being detected, so it has shut down for safety.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board (PCB)
E.04 .13

Your boiler is struggling to clear air properly because the internal fan is either stuck or spinning too fast.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
E.04 .17

Your boiler has detected an electrical issue with the component that manages the gas flow, meaning it cannot safely ignite or produce heat.

High Engineer only £200-350

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Wiring harness
E.04 .18

Your boiler has detected that the water temperature is too low or a sensor has become disconnected, causing it to shut down to prevent potential damage.

High Engineer only £150-250

Parts commonly replaced

  • NTC flow temperature sensor
  • Wiring harness

Related codes

E.04 .23

Your boiler has lost the ability for its internal parts to talk to each other, so it has shut down to prevent errors.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
Showing 41–50 of 66
E.04 .29

Your boiler's electronic parts are temporarily struggling to talk to each other, which has caused the system to stop working as a safety precaution.

High Engineer only £150-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
E.04 .54

Your boiler has detected an internal electrical problem with the component that manages the gas supply, so it has safely shut down to prevent unsafe operation.

High Engineer only £250-450

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Wiring harness
E.04 .254

Your boiler has detected an issue with the internal electronics that manage the fuel supply, so it has safely shut down to prevent unsafe operation.

Emergency Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Printed Circuit Board (PCB)
  • Wiring harness
E.04.03

Your boiler has detected that the water inside is running much hotter than it should be, or it is struggling to accurately measure that temperature.

High Engineer only £150-250

Parts commonly replaced

  • NTC Flow Temperature Sensor
  • Primary Heat Exchanger
E.04.10

Your boiler has tried to start up four times but failed to get the gas flame going, so it has locked itself for safety.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead

Related codes

H.00.42

Your boiler is struggling to detect the water pressure inside the system because the sensor that monitors it has stopped communicating correctly.

High Engineer only £120-220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
H.00.81

Your boiler has lost its connection to your digital wall thermostat or controller, meaning it cannot receive instructions on when to turn the heating on.

Medium DIY-safe £100-200

What to check first

  1. Check if your wall controller has batteries and replace them if they are flat.
  2. Restart your system by turning the boiler off at the fused spur for 30 seconds and turning it back on.
  3. Check if the controller has been moved or if there is interference preventing the wireless signal from reaching the boiler.

Parts commonly replaced

  • Wireless receiver unit
  • Room thermostat
  • Control PCB
H.01 .14

Your boiler is overheating because water isn't flowing through your radiators as quickly as the boiler expects.

High Engineer only £120-250

Parts commonly replaced

  • Central Heating Pump
  • System Filter
  • Diverter Valve
H.01.00

Your boiler is having a temporary communication hiccup between its internal electronic parts, which has caused it to pause operation as a precaution.

High Engineer only £120-250

Parts commonly replaced

  • Main PCB
  • Wiring harness
H.01.05

Your boiler has detected that the water leaving it is significantly hotter than the water returning, suggesting that heat isn't circulating properly through your radiators.

High DIY-safe £150-300

What to check first

  1. Check your boiler's pressure gauge to ensure it is between 1.0 and 1.5 bar
  2. If the pressure is low, top it up using the external filling loop
  3. Ensure all radiator valves are fully open and there is no trapped air by bleeding radiators

Parts commonly replaced

  • Central heating pump
  • System filter
  • Diverter valve
Showing 51–60 of 66
H.01.08

Your boiler has paused heating because the water is heating up faster than expected, likely due to a restriction in the system.

Medium DIY-safe £120-250

What to check first

  1. Check that all radiator valves throughout your home are fully open
  2. Ensure your system pressure gauge is reading between 1.0 and 1.5 bar
  3. Bleed your radiators to remove any trapped air that might be blocking water flow

Parts commonly replaced

  • System filter
  • Central heating pump
  • Plate heat exchanger
H.01.18

Your boiler has detected that water is not moving through your heating system properly and has temporarily stopped itself to prevent overheating.

High Engineer only £120-250

Parts commonly replaced

  • Central heating pump
  • System filter
  • Diverter valve
H.01.21

Your boiler is heating water too quickly, which is triggering a safety shut-down to prevent the system from overheating.

Medium Engineer only £120-250

Parts commonly replaced

  • Diverter valve
  • Plate heat exchanger
  • NTC thermistor sensor
H.02 .00

Your boiler is currently resetting itself after a recent issue or power interruption and should begin working normally again shortly.

Low DIY-safe

What to check first

  1. Wait 5 to 10 minutes for the boiler to complete its internal reset process.
  2. If the code persists, restart your boiler using the main power switch.
  3. Monitor the display to see if the system returns to normal operation.
H.02 .02

Your boiler is currently idle because it has not been told how to operate, usually because it was recently installed or the internal memory was reset.

High Engineer only £80-150

Parts commonly replaced

  • Electronic Control Board

Related codes

H.02 .03

Your boiler's internal computer settings have not been set up properly, which is preventing the system from running as it should.

High Engineer only £100-200

Parts commonly replaced

  • Main printed circuit board (PCB)

Related codes

H.02 .04

Your boiler's internal computer is experiencing a communication error and cannot read its own operating instructions.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Wiring harness

Related codes

H.02 .05

Your boiler's internal computer is experiencing a conflict between its settings and its main control board, which has caused it to stop working for safety reasons.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Configuration Key

Related codes

H.02 .09

Your boiler has detected an external safety signal or an internal settings error, causing it to shut down for protection.

High Engineer only £120-250

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • External controls interface

Related codes

H.02 .10

Your boiler has detected an external safety device or switch has been triggered, causing it to shut down to protect your home.

High Engineer only £120-250

Parts commonly replaced

  • External safety interlock
  • Wiring loom
  • Control PCB

Related codes

Showing 61–66 of 66
H.02 .70

Your boiler is having trouble communicating with an add-on accessory, likely an external unit or control device, preventing it from functioning correctly.

High Engineer only £150-300

Parts commonly replaced

  • SCB-09 circuit board
  • External wiring harness
  • Communication cable

Related codes

H.02.07

Your boiler has lost the water pressure it needs to circulate heat around your home, so it has turned itself off to prevent damage.

High DIY-safe £80-150

What to check first

  1. Locate the external filling loop, usually a small silver braided hose with one or two valves located underneath the boiler.
  2. Slowly open the valve(s) to allow mains water into the heating system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.
  3. Close the valve(s) tightly to ensure no water continues to enter the system.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Expansion vessel
H.03 .00

Your boiler has lost communication with its internal safety components, meaning it cannot safely operate and has disabled itself to prevent potential risks.

High Engineer only £300-500

Parts commonly replaced

  • Main PCB
H.03 .05

Your boiler is struggling because the electricity supply it is receiving is weaker than it should be.

Medium Engineer only £100-£200

Parts commonly replaced

  • PCB
  • Wiring harness

Related codes

H.03 .54

Your boiler has shut down because it keeps losing its flame, possibly due to a problem with the internal sensor that detects it or an unstable electricity supply.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB
H.03.02

Your boiler has briefly lost its flame, but it is likely attempting to restart itself automatically; if it stays off, it indicates a recurring issue with the ignition or gas supply.

Medium Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe

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