BoilerFaultCodesThe 5 most common faults
01
B High DIY-safe
Your boiler has stopped working because the water pressure inside the system is too low or the internal water pump is struggling.
What to try first
Check the pressure gauge on the front of your boiler to see if it has dropped below 1 bar.Locate the filling loop valves underneath your boiler.Open the valves gently to let water in until the pressure gauge rises to between 1 and 1.5 bars, then close them tightly.
02
D High Engineer
Your boiler has temporarily shut down because the internal water temperature has gotten too hot.
Full guide for D03
E High Engineer
Your boiler has tried to start up, but the gas failed to ignite properly.
Full guide for E04
A Emergency Engineer
Your boiler has detected a blockage or restriction in the flue pipe that carries exhaust gases safely outside your home.
Full guide for A05
C Medium Engineer
Your boiler has temporarily stopped working because it cannot accurately read how hot the water is inside the system.
Full guide for Con the Main Combi 24
Circulating pumpPressure relief valvePressure sensorAutomatic bypass valveNTC thermistorIgnition electrode
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