Atag A200 Fault codes & diagnostics

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

Combi Natural Gas 20-35 kW 2008-2016 Discontinued

Replaced by: iC Economiser

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
49 High 9 Medium 17 Low
Just want the most common Atag A200 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 75 documented codes

Tap any card for details

LED / flash-pattern codes
FILL (flashing)

Your boiler has detected that the water pressure is too low to operate at full capacity and simply needs more water added to the system.

Medium DIY-safe £0-80

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.
  2. Slowly open the valve(s) to allow water into the system while watching the pressure display.
  3. Close the valves firmly once the pressure reaches between 1.2 and 1.5 bar.

Parts commonly replaced

  • External filling loop
  • Pressure sensor

Related codes

Full explanation for FILL (flashing)
Digital codes
10

Your boiler is having trouble reading the outdoor temperature, which may cause your heating to behave unpredictably or run at the wrong temperature.

Low Engineer only £90-180

Parts commonly replaced

  • Outside weather compensation sensor
  • Sensor wiring harness
Full explanation for 10
20

Your boiler has lost its ability to accurately measure the temperature of the water leaving the unit, usually due to a faulty sensor or a wiring issue.

High Engineer only £120-£200

Parts commonly replaced

  • Flow NTC sensor
  • Wiring harness
  • Control PCB

Related codes

Full explanation for 20
40

Your boiler has lost signal from the pipe that monitors water returning to the unit, causing the heating to stop working for safety.

High Engineer only £90-180

Parts commonly replaced

  • Return temperature sensor (NTC)
  • Connecting wiring harness

Related codes

Full explanation for 40
50

Your boiler has detected a problem with the sensor that manages your hot water, which usually means it cannot heat water safely or accurately.

High Engineer only £90-160

Parts commonly replaced

  • DHW NTC thermistor (T3 sensor)
  • Sensor wiring harness

Related codes

Full explanation for 50
61

Your boiler is having trouble communicating internally with its control components, meaning it cannot currently receive instructions to heat your home.

High Engineer only £120-450

Parts commonly replaced

  • Wiring harness
  • Main PCB
  • Internal bus controller
Full explanation for 61
78

Your boiler has detected that the water pressure is either too low or too high to operate safely, or the sensor that monitors this pressure has lost its connection.

High DIY-safe £90-180

What to check first

  1. Check the pressure gauge on the front of the boiler or via the display menu.
  2. If the pressure is below 1.0 bar, use the filling loop valves to top it up to roughly 1.5 bar.
  3. If the pressure is too high (above 3.0 bar), bleed a radiator to release some water and lower the pressure.
  4. Restart the boiler to see if the code clears.

Parts commonly replaced

  • Water pressure sensor
  • Filling loop
  • Expansion vessel

Related codes

Full explanation for 78
105

Your boiler has detected low water pressure and is now running a pre-programmed automatic cycle to clear any air bubbles from the pipes.

Low DIY-safe

What to check first

  1. Check the pressure gauge is between 1.0 and 1.5 bar
  2. If pressure is low, top it up using the filling loop
  3. Wait 7 to 10 minutes for the internal air-clearing program to finish automatically

Related codes

Full explanation for 105
110

Your boiler has switched itself off because it has detected that the water inside has become far too hot.

High DIY-safe £120-£350

What to check first

  1. Check that your radiator valves are fully open to allow water to flow.
  2. Ensure your system 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

  • Circulation Pump
  • Overheat Thermostat
  • Main Heat Exchanger (Flushing)

Related codes

Full explanation for 110
117

Your boiler has shut down because there is too much water pressure in the system, which needs to be lowered to a safe level.

High DIY-safe £0-120

What to check first

  1. Locate a radiator bleed valve and use a radiator key to carefully release a small amount of water into a container.
  2. Monitor the pressure gauge on the boiler until it drops back into the green zone, typically between 1.0 and 1.5 bar.
  3. Check that the filling loop valves are fully closed to prevent more water from entering the system.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for 117
Showing 11–20 of 75
118

Your boiler has detected that the water pressure is too low, causing it to slow down and lose efficiency to protect its internal parts.

Medium DIY-safe £0-120

What to check first

  1. Locate the filling loop (the flexible silver hose usually found underneath the boiler).
  2. Open the small black valve(s) slowly until you hear water entering the system.
  3. Watch the pressure gauge and close the valve(s) tightly once the reading reaches 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for 118
119

Your boiler has lost its connection to an external safety device or a manual bridge circuit, causing it to shut down for safety.

High Engineer only £90-180

Parts commonly replaced

  • Bridge Link Wire
  • External Limit Thermostat
  • Safety Circuit Cable

Related codes

Full explanation for 119
129

Your boiler has stopped working because the internal fan, which safely exhausts fumes, isn't starting up.

High Engineer only £280-450

Parts commonly replaced

  • Combustion Fan
  • PCB (Control Board)
  • Wiring harness

Related codes

Full explanation for 129
133

Your boiler has failed to light after several tries, meaning you will not have any heating or hot water until the issue is resolved.

High DIY-safe £100-350

What to check first

  1. Check that your gas emergency control valve is in the 'on' or open position
  2. If you have a prepayment meter, verify that you have sufficient credit
  3. Reset the boiler by pressing the 'Reset' button on the control panel to see if it clears the lockout

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Probe
  • Condensate Trap (if blocked)

Related codes

Full explanation for 133
151

Your boiler has shut down because it cannot control the fan that safely clears exhaust gases, or the internal control board has developed a fault.

High Engineer only £250-£650

Parts commonly replaced

  • Fan assembly
  • PCB (Main control board)
  • Wiring harness

Related codes

Full explanation for 151
154

Your boiler has detected that water is not circulating correctly through the system, causing it to shut down to prevent overheating.

High DIY-safe £120-350

What to check first

  1. Check that the boiler pressure is between 1.0 and 1.5 bar
  2. Ensure all radiator valves and isolation valves are fully open
  3. Bleed your radiators to remove any trapped air pockets
  4. Restart the boiler using the reset button

Parts commonly replaced

  • Circulation pump
  • Return thermistor
  • Main heat exchanger (cleaning/flushing)

Related codes

Full explanation for 154
180

This is a normal confirmation message that appears briefly when your boiler finishes a standard maintenance test and returns to normal operation.

Low DIY-safe

What to check first

  1. No action is required; the code should disappear on its own within a few seconds.
  2. If the code persists, try restarting the boiler using the reset button.
  3. Ensure the 'Chimney Sweep' or 'Service' mode hasn't been accidentally left active.

Related codes

Full explanation for 180
181

This is a normal message showing that your boiler has successfully finished its setup or maintenance checks and is returning to normal operation.

Low DIY-safe

What to check first

  1. No action is required
  2. Wait a few seconds for the code to disappear
  3. Confirm the boiler returns to its standard temperature display
Full explanation for 181
A xx

Your boiler is currently running a routine air-removal cycle to ensure the system is clear of air bubbles, which is a normal process after a restart or refill.

Low DIY-safe

What to check first

  1. Wait 17 minutes for the cycle to complete automatically
  2. Ensure all radiator valves are open to help move air through the system
  3. Once finished, the boiler should return to normal operation without intervention

Related codes

Full explanation for A xx
A0

Your boiler has identified an issue with the temperature of the water flowing through the system, meaning it has temporarily switched off to prevent overheating.

High Engineer only £150-300

Parts commonly replaced

  • NTC Sensor
  • Pump
  • Main Heat Exchanger

Related codes

Full explanation for A0
Showing 21–30 of 75
A1

Your boiler has detected that the water returning from your radiators is too hot, causing it to pause heating to prevent damage.

Medium Engineer only £120-250

Parts commonly replaced

  • Return NTC sensor
  • Central heating pump
  • Plate heat exchanger

Related codes

Full explanation for A1
A2

Your boiler is struggling to accurately measure or regulate the temperature of the water being sent to your taps.

Medium Engineer only £120-250

Parts commonly replaced

  • Domestic hot water sensor
  • NTC thermistor

Related codes

Full explanation for A2
A4

Your boiler has detected that the exhaust gases leaving the system are running hotter than they should be.

High Engineer only £150-300

Parts commonly replaced

  • Flue gas sensor
  • Heat exchanger
  • Burner seal

Related codes

Full explanation for A4
A5

Your boiler is struggling to detect the outdoor temperature, but it will continue to heat your home using its internal settings as a backup.

Low Engineer only £100-200

Parts commonly replaced

  • Outside temperature sensor
  • Wiring loom
Full explanation for A5
A6

Your boiler has detected that the water pressure inside the system is currently too low to operate safely.

High DIY-safe £80-120

What to check first

  1. Locate the filling loop (a silver flexi-hose) beneath the boiler.
  2. Open the valves on the filling loop to allow cold mains water into the system.
  3. Watch the pressure gauge on the boiler until the needle reaches between 1.0 and 1.5 bar, then securely close the valves.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor
  • Expansion vessel

Related codes

Full explanation for A6
A9

Your boiler is struggling to spin the internal fan that clears out exhaust gases, so it has safely shut down to prevent unsafe operation.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • PCB
Full explanation for A9
Block 01

Your boiler has shut down because an external safety device or a control loop has detected an issue and cut the circuit to prevent damage.

High Engineer only £90-180

Parts commonly replaced

  • External Limit Thermostat
  • Safety Loop Bridging Wire
  • System Pump

Related codes

Full explanation for Block 01
Block 11

Your boiler is overheating because the water is not flowing through the system quickly enough to take the heat away.

Medium DIY-safe £100-350

What to check first

  1. Check that all radiator valves are fully open including the lockshield valves
  2. Ensure there are no blockages in the magnetic system filter if one is fitted
  3. Check that the boiler pressure is between 1.0 and 1.5 bar

Parts commonly replaced

  • Circulation Pump
  • Flow and Return Sensors
  • Main Heat Exchanger (De-scaling)
Full explanation for Block 11
Block 12

Your boiler is temporarily pausing hot water production because the temperature difference between the water going out and coming back is too high, often due to a flow restriction.

Medium Engineer only £120-350

Parts commonly replaced

  • Secondary plate heat exchanger
  • Diverter valve
  • Flow/Return thermistors

Related codes

Full explanation for Block 12
Block 60

Your boiler’s internal computer has lost its correct power settings, meaning it doesn't know how high or low to run the flame.

High Engineer only £100-250

Parts commonly replaced

  • Control Board (PCB)
  • Display Unit
Full explanation for Block 60
Showing 31–40 of 75
Block 67

Your boiler has noticed an unusual temperature difference between two pipes while it isn't even running, causing it to pause for safety until the temperatures level out.

Medium Engineer only £90-180

Parts commonly replaced

  • Flow temperature sensor
  • Return temperature sensor
  • Wiring harness
Full explanation for Block 67
Block 80

Your boiler has switched itself off because the waste gases are getting too hot, which is a safety measure to prevent internal damage.

High Engineer only £150-450

Parts commonly replaced

  • Main Heat Exchanger
  • Flue Gas Sensor
  • Burner Insulation Panel

Related codes

Full explanation for Block 80
Block 81

Your boiler has stopped working because it can no longer detect a vital safety sensor that monitors exhaust gases.

High Engineer only £100-£220

Parts commonly replaced

  • Flue Gas Sensor (NTC)
  • Wiring Harness
  • Main Control PCB

Related codes

Full explanation for Block 81
Block 82

Your boiler has detected a fault with its exhaust temperature sensor and has shut down to protect itself from overheating.

High Engineer only £140-£260

Parts commonly replaced

  • Flue gas sensor (NTC)
  • Wiring harness

Related codes

Full explanation for Block 82
Block 85

Your boiler is struggling to detect water moving through the system and is currently trying to clear air from the pipes to fix itself.

High DIY-safe £100-280

What to check first

  1. Check that the boiler pressure is between 1.0 and 1.5 bar on the gauge.
  2. Ensure all radiator valves and isolation valves under the boiler are fully open.
  3. Gently bleed your radiators to remove any trapped air pockets.

Parts commonly replaced

  • Water pressure sensor
  • Circulation pump
  • Automatic air vent
Full explanation for Block 85
C 20

Your boiler is struggling to detect the flow of water through the system, which means it has safely shut down to prevent overheating.

High Engineer only £150-250

Parts commonly replaced

  • Flow sensor
  • Wiring harness
  • PCB
Full explanation for C 20
C 40

Your boiler is struggling to accurately measure the temperature of the water returning to it, which prevents the system from heating your home correctly.

High Engineer only £150-250

Parts commonly replaced

  • Return temperature sensor
  • Wiring harness
Full explanation for C 40
C 78

Your boiler is struggling to circulate water, either because there isn't enough water inside the system or because the internal pump has stopped working.

High DIY-safe £150-350

What to check first

  1. Check your boiler's pressure gauge and ensure it is between 1.0 and 1.5 bar.
  2. If the pressure is low, use the filling loop to top up the system to the correct range.
  3. Check that your heating circulating valves are open and not blocked.

Parts commonly replaced

  • Central heating pump
  • Pressure sensor
  • Expansion vessel
Full explanation for C 78
C1 10

Your boiler has detected that it is running much hotter than it should be and has automatically shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Pump
  • Heat exchanger
  • NTC sensor

Related codes

Full explanation for C1 10
Showing 41–50 of 75
C1 11

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

High Engineer only £150-300

Parts commonly replaced

  • Pump
  • Heat exchanger
  • NTC sensor

Related codes

Full explanation for C1 11
c1 17

Your boiler has stopped working because the water pressure inside the system has risen too high for it to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate a radiator in your home with a bleed valve.
  2. Place a cloth or small container under the valve.
  3. Open the bleed valve slowly to release water until the pressure gauge on the front of the boiler drops to between 1.0 and 1.5 bar.
  4. Close the bleed valve tightly once the pressure has returned to the normal range.

Parts commonly replaced

  • Pressure relief valve
  • Filling loop
  • Pressure sensor
Full explanation for c1 17
c1 18

Your boiler has detected that the water pressure inside the heating system has dropped too low, so it is running at a reduced level to protect itself.

Medium DIY-safe

What to check first

  1. Locate the filling loop (usually a silver flexible hose) connected to your boiler pipes.
  2. Open the valves on the filling loop slowly to let water into the system.
  3. Watch the pressure gauge on the front of the boiler until the needle reaches the green zone, typically between 1.0 and 1.5 bar.
  4. Close both valves tightly and remove the filling loop if it is not a permanent fixture.

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor (transducer)
  • Expansion vessel

Related codes

Full explanation for c1 18
C1 29

Your boiler's air circulation system isn't starting, which prevents the unit from firing up safely to provide heat or hot water.

High Engineer only £200-350

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Control board
Full explanation for C1 29
C1 33

Your boiler has failed to light the flame after several attempts and is currently unable to provide heating or hot water.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition transformer
Full explanation for C1 33
C1 51

Your boiler is unable to safely vent exhaust gases because the internal fan is not spinning at the required speed.

High Engineer only £250-450

Parts commonly replaced

  • Fan unit
  • Wiring harness
  • PCB
Full explanation for C1 51
c1 54

Your boiler is struggling to pump water around your heating system correctly and has shut down to prevent itself from overheating.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • Flow sensor
  • NTC thermistor
Full explanation for c1 54
C123

Your boiler is displaying a service notification indicating that a technician is attempting to enter or has entered the password-protected installer settings menu.

Low DIY-safe £0-80

What to check first

  1. Press the 'Reset' or 'Back' button to return to the main display
  2. Monitor the screen to see if the code clears and the heating continues as normal
  3. If the code persists, restart the boiler using the power isolation switch

Related codes

Full explanation for C123
COdE

Your boiler is asking for a security pin code to access the installer settings menu and is not currently showing an actual fault.

Low Engineer only £60-120
Full explanation for COdE
E01

Your boiler has failed to ignite and cannot produce heating or hot water, likely because it has tried to light several times without success.

High DIY-safe £100-£250

What to check first

  1. Check if other gas appliances, like a gas hob, are working to ensure your gas supply is active.
  2. If you have a prepaid gas meter, verify that you have enough credit.
  3. Press and hold the 'Reset' button on the boiler control panel for several seconds to restart the ignition sequence.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Ionisation Probe

Related codes

Full explanation for E01
Showing 51–60 of 75
E02

Your boiler has detected an ignition failure or a flame loss, meaning it is unable to stay lit to provide heating or hot water.

High DIY-safe £120-350

What to check first

  1. Check that your gas prepayment meter has credit (if applicable)
  2. Check that other gas appliances, such as a hob, are working to confirm gas supply
  3. Press and hold the 'Reset' button for 2 seconds to see if the boiler restarts

Parts commonly replaced

  • Ignition electrode
  • Flame sensing probe
  • Gas valve

Related codes

Full explanation for E02
E03

Your boiler has stopped heating because one of its internal temperature sensors is reporting an unusual reading or has failed.

High Engineer only £100-180

Parts commonly replaced

  • Flow temperature NTC sensor
  • Wiring harness

Related codes

Full explanation for E03
E04

Your boiler has detected an issue with the sensor that monitors water returning from your radiators, which may stop the system from heating effectively.

High DIY-safe £120-220

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure there is enough water pressure in the system (typically 1.0 to 1.5 bar on the gauge)
  3. Attempt to reset the boiler using the 'Reset' button

Parts commonly replaced

  • NTC Return Temperature Sensor
  • Connecting wiring harness

Related codes

Full explanation for E04
E05

Your boiler has detected an internal electrical communication error or a control board fault, preventing it from heating your home.

High Engineer only £250-550

Parts commonly replaced

  • Main PCB (Control Board)
  • Wiring Loom

Related codes

Full explanation for E05
E06

Your boiler is likely shutting down because it has detected an issue with the water pump, meaning the internal water isn't circulating correctly to provide heat.

High Engineer only £220-450

Parts commonly replaced

  • Circulation Pump
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E06
Err.L

Your boiler is displaying a saved history of the most recent technical faults encountered rather than an active problem that requires an immediate fix.

Low DIY-safe

What to check first

  1. Press the Reset button once to clear the menu from the display
  2. If the boiler is working normally, no further action is required
  3. Monitor the screen to see if a specific error code (like C, E, or 1) appears after resetting
Full explanation for Err.L
Err.L - Err.5

Your boiler is displaying a saved history of its most recent malfunctions to help a technician diagnose recurring issues.

Low DIY-safe £0-80

What to check first

  1. Press the 'Reset' button to clear the current display
  2. Scroll through the menu to view previous fault codes for reference
  3. Monitor the boiler to see if a specific active fault code returns
Full explanation for Err.L - Err.5
Error 00

Your boiler is struggling to light or maintain a steady flame, which means it cannot heat your home safely and has shut down as a precaution.

High Engineer only £120-£350

Parts commonly replaced

  • Ionisation probe
  • Ignition electrode
  • Gas valve
  • Condensate trap

Related codes

Full explanation for Error 00
Error 01

Your boiler has experienced an internal electrical fault that has caused it to shut down to prevent damage to its control system.

High Engineer only £120-350

Parts commonly replaced

  • Low voltage wiring harness
  • External sensors
  • Printed Circuit Board (PCB)

Related codes

Full explanation for Error 01
Error 02

Your boiler is failing to light the gas, meaning it cannot produce any heat or hot water.

High DIY-safe £120-350

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas supply is active
  2. Ensure your gas meter has credit if you use a pre-payment meter
  3. Press the Reset button on the boiler control panel once

Parts commonly replaced

  • Ignition electrode
  • Flame sensing probe
  • Gas valve
  • PCB

Related codes

Full explanation for Error 02
Showing 61–70 of 75
Error 04

Your boiler has experienced a power supply interruption or an electrical signal issue, causing it to shut down for safety.

High DIY-safe £0-250

What to check first

  1. Check if there has been a recent power cut or if a fuse has tripped in your home electrical consumer unit.
  2. Restart the boiler by pressing the 'Reset' button on the control panel.
  3. Ensure all electrical cables leading to the boiler are securely plugged in and the isolation switch is turned on.

Parts commonly replaced

  • Fuses
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for Error 04
Error 05

Your boiler is having trouble managing its internal settings during the startup process and cannot calibrate the flame correctly.

High Engineer only £120-280

Parts commonly replaced

  • Ionisation probe
  • Gas valve
  • Electrode
Full explanation for Error 05
Error 12

Your boiler has lost power to its internal control system due to a blown fuse, which has caused the unit to shut down completely.

High Engineer only £90-180

Parts commonly replaced

  • 3.15A Fast Blow Fuse
  • Internal Wiring Harness
  • Low Voltage Transformer
Full explanation for Error 12
Error 18

Your boiler has shut down because the water inside it has become too hot for safe operation.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate.
  2. Inspect the boiler pressure gauge and top up to 1.5 bar if it is too low.
  3. Restart the boiler using the reset button to see if the fault clears.

Parts commonly replaced

  • Circulation pump
  • Flow temperature sensor (NTC)
  • Main Heat Exchanger (Deep clean/Flush)

Related codes

Full explanation for Error 18
Error 19

Your boiler has shut down because the water returning from your radiators is too hot, meaning heat is not being released into your home properly.

High DIY-safe £100-350

What to check first

  1. Check that at least two or three radiator valves (TRVs) are turned to the maximum setting.
  2. Ensure your room thermostat is set higher than the current room temperature.
  3. Check that all radiator valves are physically open and not stuck in the closed position.

Parts commonly replaced

  • Circulation pump
  • Return temperature sensor (NTC)
  • Bypass valve

Related codes

Full explanation for Error 19
Error 28

Your boiler has stopped working because the internal fan is not communicating correctly with the main control system.

High Engineer only £220-£450

Parts commonly replaced

  • Extraction Fan
  • Wiring Harness
  • Main Control PCB
Full explanation for Error 28
Error 69

Your boiler is still working to provide heat and hot water, but the control panel display is either blank or showing scrambled information.

Low Engineer only £120-300

Parts commonly replaced

  • Display PCB
  • Ribbon cable connection
  • Main Control Board
Full explanation for Error 69
Error 80

Your boiler has shut down because the exhaust gases have become too hot, which is a safety measure to prevent damage to the internal components.

High Engineer only £150-350

Parts commonly replaced

  • Flue Gas Sensor (NTC)
  • Heat Exchanger (cleaning/descaling)
  • Main Heat Exchanger

Related codes

Full explanation for Error 80
F1

Your boiler is notifying you that a specific brand of system protector or anti-freeze chemical has been detected in the water to help prevent internal corrosion and freezing.

Low DIY-safe £0-80

What to check first

  1. Press the Reset button on the control panel
  2. Monitor the display to see if the code clears
  3. If the code persists, check your system pressure is between 1.0 and 1.5 bar

Parts commonly replaced

  • None
  • Fernox F1 Protector (Top-up)
Full explanation for F1
FILL

Your boiler has detected that the water pressure is too low to operate properly and needs to be topped up.

Medium DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath your boiler.
  2. Open the one or two taps/levers on the filling loop until you hear water moving.
  3. Watch the pressure gauge on the screen and close the taps once the pressure reaches between 1.2 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for FILL
Showing 71–75 of 75
Good

Your boiler is working perfectly and is currently operating without any detected faults or issues.

Low DIY-safe

What to check first

  1. No action is required.
  2. The 'Good' message is the normal status display for an Atag boiler in operation.
Full explanation for Good
HIGH

Your boiler has too much water inside it, causing the pressure to rise to an unsafe level that has shut the system down.

High DIY-safe £0-120

What to check first

  1. Check that the filling loop valves are fully closed and not leaking water into the system
  2. Locate a radiator bleed valve and use a key to drain a small amount of water into a container
  3. Monitor the pressure gauge until it falls between 1.0 and 1.5 bar
  4. Press the reset button to restart the boiler

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve
Full explanation for HIGH
P x.x

Your boiler is displaying its current water pressure; if it stays on this screen, the pressure may be too high or too low for the system to run.

Low DIY-safe £0-120

What to check first

  1. Locate the filling loop (the silver braided hose) underneath the boiler.
  2. Slowly open the valves until the pressure reading on the screen reaches between 1.2 and 1.5 bar.
  3. Close the valves completely and ensure the display no longer flashes.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for P x.x
StBY

Your boiler is currently idle because it has reached its set temperature or there is no active request for heating or hot water.

Low DIY-safe

What to check first

  1. Check that your room thermostat is turned up higher than the current room temperature.
  2. Ensure your programmer or heating app is set to an 'On' period.
  3. Verify that the boiler's target temperature settings haven't been turned down too low.
Full explanation for StBY
STOP

Your boiler has reached the correct water pressure while being topped up and is letting you know the filling process is complete.

Low DIY-safe

What to check first

  1. Locate the filling loop valves (usually chrome handles) under the boiler.
  2. Ensure both valves are turned to the fully closed position.
  3. Check that the 'STOP' message has cleared and the boiler returns to its normal pressure reading.

Related codes

Full explanation for STOP