BoilerFaultCodesThe 6 most common faults
01
4 High DIY-safe
Your boiler has tried to light itself four times but has failed, so it has locked itself out for safety.
What to try first
Check that your gas emergency control valve (gas tap) is in the 'on' positionEnsure you have credit on your gas meter if you use a prepay systemCheck other gas appliances like a hob to see if there is a gas supply to the houseCheck that the white plastic condensate pipe outside hasn't frozen in cold weatherPress the 'Reset' button on the boiler control panel
02
5 High DIY-safe
Your boiler is failing to stay alight because it cannot safely ignite the gas or clear away waste water.
What to try first
Check if the condensate pipe (the plastic pipe running outside) is frozen or blocked.Carefully thaw a frozen external pipe with warm—not boiling—water.Restart the boiler by pressing the reset button to see if it ignites.
03
6 High Engineer
Your boiler is failing to light the gas or cannot identify that a flame is present, meaning your heating and hot water will not work.
Full guide for 604
8 High Engineer
Your boiler has stopped working because the fan that helps remove exhaust gases isn't spinning at the correct speed.
Full guide for 805
10 High Engineer
Your boiler has stopped working because one of its internal heat sensors is no longer sending a reliable signal to the main control board.
Full guide for 1006
11 High Engineer
Your boiler has detected a problem with its primary internal temperature sensor, meaning it cannot safely monitor the heat of the water and has stopped running as a precaution.
Full guide for 11on the Atmos Interopen HE22
Ignition ElectrodeGas ValveIgnition TransformerFlame SensorIgnition electrodeGas valve
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