BoilerFaultCodesThe 6 most common faults
01
27 High DIY-safe
Your boiler is struggling because it either cannot circulate water correctly or there is not enough water pressure inside the system to operate safely.
What to try first
Check the system pressure gauge on the front of the boiler; if it is below 1 bar, locate the filling loop.Open the filling loop valves to top up the system until the needle reaches 1.5 bar, then ensure the valves are tightly closed.Restart the boiler to see if the fault clears.
02
24 High Engineer
Your boiler has stopped working because it cannot light its burner properly, which is often due to a blockage in the internal waste pipe that clears away water created during heating.
Full guide for 2403
26 High Engineer
Your boiler is struggling to clear air properly, meaning it has safely shut itself down to prevent any harmful combustion gases from lingering.
Full guide for 2604
29 High Engineer
Your boiler has stopped working because it is unable to accurately measure the temperature of the water used for your radiators.
Full guide for 2905
E66 High Engineer
Your boiler is struggling to direct heat correctly between your radiators and your hot water taps, likely due to a stuck internal component or a sensor reading error.
Full guide for E6606
10 High Engineer
Your boiler has lost the ability to accurately measure the temperature of the hot water, so it has shut down to prevent overheating.
Full guide for 10on the Main Combi 30 HE
Circulation pumpPressure sensorExpansion vesselCondensate trapIgnition 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 Main 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