AWB boiler faults: fault codes, causes and parts

All 436 fault codes for AWB boilers, plus the faults that show no code. Type your code or choose your symptom.

In brief

A fault on an AWB boiler usually means that the appliance has locked out or is reporting a fault code. Note the code on the display and look it up below: for each code you will find its meaning, checks you can safely do yourself and the parts that are often checked or replaced. Frequently searched: 24 (return temperature > 90°C), E (pump control circuit fault), 3.1 (flow NTC short-circuited). No code? Check the water pressure (1.5 to 2 bar when cold), the power supply and the gas tap, and reset once. If the fault comes back, call in a certified gas engineer. If you smell gas, call your national gas emergency number or 112 immediately.

Most searched AWB faults

These are the codes that visitors to this site search for most often.

24Return temperature > 90°C. Insufficient or no…EPump control circuit fault 3.1Flow NTC short-circuited.F4A defective DHW sensor.F9Water pressure sensor fault. Check the wiring F 14Flow temperature greater than 95 C LAir pressure switch switches off during operation F11Defective temperature sensor in the CH flow…

See the 25 most searched fault codes of 2026, with the figures behind them →

AWB boiler faults without a code on the display

Not every fault shows a code. These are the symptoms we come across most often with AWB appliances, with what you can check yourself before calling someone out.

No hot water, but the heating works

The boiler heats the radiators but not the tap water. Check that the hot water function is switched on in the display (on some appliances it is called DHW mode or summer mode) and that the hot water valve under the boiler is open. If the water stays cold, this usually points to a fouled or leaking DHW heat exchanger, a faulty diverter valve or a DHW sensor giving incorrect readings. View the matching parts → Read the full explanation: no hot water, six causes →

Water pressure keeps dropping

Top up to 1.5–2 bar when cold and bleed the radiators. If the pressure drops again within a few days, the expansion vessel has often lost its pre-charge or there is a small leak in the system. A pressure relief valve that keeps dripping gives the same symptom. View the matching parts → Read the full explanation: water pressure keeps dropping – expansion vessel or leak? →

Boiler shuts down and locks out

The appliance shuts down and only starts again after a reset. Reset once; if the fault comes straight back, leave the reset button alone. Repeatedly resetting a locked-out boiler is not without risk: the safety device trips for a reason. View the matching parts → Read also: is the boiler cutting out because of a sensor or overheating? →

Radiators stay cold

Check that the thermostat is calling for heat, that the radiator valves are open and that the system has enough pressure. If everything stays cold while the boiler is firing, the circulation pump is often not running or the diverter valve is stuck in the hot water position. View the matching parts → Read the full explanation: radiators stay cold →

Ticking, humming or boiling noise

A banging noise at start-up usually points to air or limescale in the heat exchanger. A humming pump may have a worn bearing. A rattling fan is often rubbing or dirty. View the matching parts → Read also: replacing the fan – what to rule out first →

Water under the boiler

Check where it is coming from: the condensate drain (siphon blocked or cracked), the pressure relief valve (pressure too high or faulty expansion vessel) or a fitting. If in doubt, switch the boiler off and close the water supply. View the matching parts → Read the full explanation: water under the boiler – condensate or a leak? →

AWB boiler fault codes 1 to 150 of 436

The code list is split over 3 pages. Looking for a specific code? Use the search at the top of this page: it searches all 436 codes in one go.

Code	Cause
---	User interface fault
---	Waiting time after DHW demand (2 min.)
0	Flame present when it should not be
0	Standby
0.0	Ionisation fault in standby.
0.1	Short circuit in 24 V circuit.
0.2	Ionisation fault during operation
0.3	Internal fault mcba.
0.4	Internal fault mcba.
0.5	Internal fault mcba.
0.6	See fault 05.
0.7	See fault 03.
0.8	Air pressure switch does not close.
0.9	See fault 05.
00	No fault
01	Ignition fault
02	Fan fault
03	Repeated air fault: fan keeps running below the start speed.
03	No tacho signal
04	Ignition fault
04	See F 01
05	Maximum limit fault, flow temperature too high
06	Flow NTC fault. NTC is broken or wiring faulty. Check wiring or replace NTC.
07	DHW NTC fault. NTC is broken or wiring faulty. Check wiring or replace NTC.
08	Cylinder NTC fault
09	Water pressure sensor broken or wiring faulty
1	Water pressure switch open
1.0	See fault 05.
1.1	Communication error.
1.2	Internal fault mcba.
1.3	See fault 05
1.4	Internal fault mcba.
1.5	See fault 05.
1.6	See fault 05.
1.7	See fault 03.
1.8	Flow temperature too high.
1.9	Return temperature too high.
10	Return NTC
101	24 V short circuit
11	No signal on main board. Check wiring and user interface. If in order, replace the main board. Fan defect. Replace fan
12	No signal on user interface
13	Incorrect cylinder setting parameter / main board fault
14	Flow temperature greater than 95°C
15	Stepper motor fault diverter valve
16	Incorrect flame detection
17	Insufficient mains voltage < 170 V ~
17 F	Insufficient mains voltage < 170 V ~ Faulty fuse Check the transformer, fuse and wiring. Replace the transformer if necessary Faulty main PCB Replace main PCB
18	(no change)
18	There is a fault in the user interface.
19	Flow NTC fault, dT > 35K 10 times in succession
2	Air pressure switch not in rest position
2.1	Flow temperature deviation.
2.2	Return temperature deviation.
2.4	Return temperature higher than flow temperature.
2.5	See fault 18.
2.6	Short circuit in wiring harness.
2.8	No feedback from fan to mcba.
2.9	See fault 28.
20	Software not compatible
20 F	Software not compatible
202	No flame formation
21	System water pressure too low
21 F	System water pressure too low
22	System water pressure too high
22 F	System water pressure too high
24	Return temperature > 90°C. Insufficient or no circulation. See F 5. System resistance too high, bypass insufficient.
24 F	Return temperature > 90 C Insufficient See F 05 circulation or system resistance too high, no circulation bypass insufficient
25	Rise in flow temperature too fast
25	Flow temperature rising too quickly. See F 05. System resistance too high, bypass insufficient
25 F	Rise in flow temperature too fast See F 05 System resistance too high, bypass insufficient
26	Temperature difference between flow and return temperature too large in central heating mode
26	Temperature difference between flow and return temperature too large in CH mode.
26 F	Temperature difference between flow and return temperature too large in central heating mode See F 05 System resistance too high, bypass insufficient
3	Air pressure switch does not switch on (after 120 sec.)
3.0	See fault 18.
3.1	Flow NTC short-circuited.
3.2	Return NTC short-circuited.
3.6	Flow NTC open circuit.
3.7	Return NTC open circuit.
4	CH temperature sensor NTC defective
4.1	See fault 05.
4.2	See fault 05.
4.3	See fault 05.
4.4	See fault 05.
403	Control fault
404	Control fault
405	Control fault
406	Control fault
407	Control fault
410	Control fault
411	Control fault
413	Control fault
414	Control fault
415	Control fault
416	Control fault
417	Control fault
424	Control fault
426	Control fault
429	Control fault
430	Control fault
431	Control fault
432	Control fault
436	Control fault
437	Control fault
441	Control fault
5	DHW temperature sensor NTC defective
508	Air transport
528	Air transport
6	Gas valve defective
6.0	Internal fault mcba.
6.1	Air pressure switch not in rest position.
8	Internal fault
9	Dipswitch 3 not in correct position
912	Maximum limit/water shortage
918	Maximum limit/water shortage
919	Maximum limit/water shortage
925	Maximum limit/water shortage
A	Gas valve control circuit fault
B	Cylinder demand (only for 23.38W with cylinder)
C	CH demand
C.	Control stop: CH water temperature higher than set value
E	Pump control circuit fault
E 05	Communication error on central control of the modules
E 101	The specified number of modules does not match the number of modules detected
E 11	Communication error on the boiler bus (X7) flat cable faulty or poorly connected, central control of the faulty module.
E 15	Fault in the central control MBD of the modules.
E 18	The temperature in the boiler outlet pipe is > 95 C. heating due to heat demand, but no heat being drawn off (e.g. because the cylinder charging pump is faulty).
E 19	The temperature in the boiler outlet pipe is > 95 C. heating due to heat demand, but no heat being drawn off (e.g. because the cylinder charging pump is faulty).
E 26	Open circuit at the air pressure switch, low water pressure protection or selector switch (terminals 23/24). Is the system working pressure correct? (2 bar)
E 31	Short circuit in the boiler's global flow temperature sensor (NTC). Faulty cable, poor connector contact, moisture, faulty NTC.
E 32	Short circuit in the boiler's global flow temperature sensor (NTC). Faulty cable, poor connector contact, moisture, faulty NTC.
E 36	Short circuit in the boiler's global flow temperature sensor (NTC). Faulty cable, poor connector contact, moisture, faulty NTC.
E 37	Open circuit at the temperature sensor (NTC) in the boiler return pipe
E 43	EEPROM fault
E 60	Parameters outside the permitted control range
E 90	Detection of the controller interface (AM4) impossible
E 91	Detection of the expansion board of the central boiler control.
E 92	Fault on all modules
F	Pump switched on at 7C contact
F 0	No fault
F 1	Ignition fault
F 1	Ignition fault. No flame detection No gas / gas valve closed: Check the gas connection / gas valve and the inlet pressure. No ignition: Check the ignition electrode and wiring.
F 10	Return NTC is broken or wiring faulty
F 10	Return NTC
F 11	No signal on main board. Check wiring and user interface. If in order, replace the main board. Fan defect. Replace fan
F 11	No signal on main board Check wiring and user interface. If in order, replace the main board. Fan fault.
F 11	No signal on main board Check wiring and user interface. If in order, replace the main board. Fan fault. Replace fan
F 11	No signal on main board Check wiring and user interface. If in order, replace the main board. Fan fault. Replace fan
F 12	No signal on user interface Check wiring and main board. If in order, replace the user interface.
F 12	No signal on user interface Check wiring and main board. If in order, replace the user interface.

Order parts for your AWB boiler

AWB parts are available from Instalpunt; shipping to EU countries from €12.95 (€16.95 for more distant countries), usually 3–5 working days.

View AWB parts →

Frequently asked questions about AWB faults

What does a fault on an AWB boiler mean?

The appliance is reporting that it has shut itself down or cannot continue. The code on the display points to the group of causes: ignition, water pressure, a sensor, the fan or communication with the thermostat. The table above shows, for each code, what AWB means by it.

How do I reset my AWB boiler?

The reset button is on the control panel of your AWB boiler; on most appliances you hold it down for two to five seconds until the display responds. Reset once. If the same fault comes straight back, resetting will not solve it and a part or a setting needs attention. Always consult the manual for your model: the position of the button and how long to press it differ per series.

Can I fix an AWB fault myself?

You can top up the water pressure, bleed the system, replace filters and clean a siphon yourself. Anything behind the sealed section of a gas appliance is a different matter: work on the gas valve, burner, heat exchanger and flue must be carried out by a certified gas engineer.

How much does it cost to fix a fault?

That depends on the cause and whether a part is needed. With us you can see the part straight away with its price and delivery time, so you know where you stand in advance. If you call in an engineer, always ask about the call-out charge and hourly rate before they come.

Where can I find the right part for my AWB?

Check the rating plate for the exact type and use it to search our catalogue, or search directly by the manufacturer number of the faulty part. Each part lists the appliances it fits.