BoilerFaultCodesThe 6 most common faults
01
E10 High DIY-safe
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
What to try first
Locate the external filling loop, which is usually a flexible silver braided hose with one or two valves located underneath the boiler.Open the valve(s) slowly to allow mains water into the heating system while watching the pressure gauge on the front of the boiler.Close the valve(s) tightly once the needle on the gauge reaches the green zone, typically between 1.0 and 1.5 bar.
02
E01 High Engineer
Your boiler has failed to light the flame needed to heat your water and radiators.
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 its own water temperature, so it has safely shut down to prevent overheating.
Full guide for E0505
E06 High Engineer
Your boiler is struggling to accurately measure the temperature of the hot water it produces, so it has turned off the hot water supply to prevent overheating.
Full guide for E0606
E16 High Engineer
Your boiler has stopped working because the internal component responsible for pushing exhaust gases out of the flue is not operating correctly.
Full guide for E16on the Alpha CB24
Filling loopPressure relief valvePressure sensorIgnition electrodeGas valvePCB
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