BoilerFaultCodesThe 6 most common faults
01
10, 11, 12, 13, 14 High Engineer
Your boiler is temporarily locked out because one of its internal temperature monitors is sending an incorrect reading.
Full guide for 10, 11, 12, 13, 1402
20, 21, 22, 23, 24 High Engineer
Your boiler has temporarily stopped working because it is getting incorrect temperature readings from one of its internal sensors.
Full guide for 20, 21, 22, 23, 2403
2 High Engineer
Your boiler is currently performing an internal safety check, which is a normal part of its startup process, but it has not progressed past this stage.
Full guide for 204
4 High Engineer
Your boiler is failing to light the internal flame needed to provide heating or hot water.
Full guide for 405
5 High Engineer
Your boiler has detected a problem with the internal sensor that monitors the heating circuit, meaning it cannot reliably provide central heating.
Full guide for 506
6 High Engineer
Your boiler is failing to detect a flame, meaning it cannot stay lit to provide heating or hot water.
Full guide for 6on the Atmos Intersystem HE40 C
NTC ThermistorTemperature SensorWiring HarnessControl BoardIgnition electrodeIgnition lead
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Atmos shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue