BoilerFaultCodesThe 6 most common faults
01
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 202
4 High Engineer
Your boiler is failing to light the internal flame needed to provide heating or hot water.
Full guide for 403
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 504
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 605
8 High Engineer
Your boiler has stopped working because the internal fan is moving at the wrong speed or cannot communicate with the main control board.
Full guide for 806
10 High Engineer
Your boiler has stopped working because one of its internal temperature sensors has detected a fault or a broken connection.
Full guide for 10on the Atmos Intersystem HE40 C
Control BoardWiring HarnessIgnition electrodeIgnition leadGas valveFlow Temperature Sensor
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