BoilerFaultCodesThe 6 most common faults
01
E04 High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
What to try first
Locate the filling loop, which is usually a flexible silver hose connected to two valves beneath the boiler.Open the valves slowly to allow mains water to enter the system while watching the pressure gauge on the front of the boiler.Close both valves firmly once the needle reaches the green zone, typically between 1.0 and 1.5 bar.
02
E01 High Engineer
Your boiler is failing to light the flame needed to produce heat and hot water.
Full guide for E0103
E02 High Engineer
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.
Full guide for E0204
E05 High Engineer
Your boiler has lost the ability to accurately measure the temperature of the water circulating through your heating system, so it has shut down as a safety precaution.
Full guide for E0505
E10 High Engineer
Your boiler has detected that the incoming gas pressure is too low to safely ignite or maintain its flame, so it has shut down to prevent issues.
Full guide for E1006
E22 High Engineer
Your boiler's internal computer memory has encountered a data error, meaning it has forgotten how to correctly control your heating and hot water.
Full guide for E22on the Alpha SY
Filling loopPressure relief valvePressure sensorIgnition leadIgnition 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 Alpha 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