BoilerFaultCodesThe 6 most common faults
01
Lockout High DIY-safe
Your boiler has stopped running as a safety precaution and needs a manual restart to try and light the flame again.
What to try first
Turn the control thermostat knob 'A' anti-clockwise to the 'RESET' (OFF) position.Wait for at least 3 minutes to allow any gas to clear.Turn the knob clockwise back to the maximum setting to restart the boiler.
02
E20 High Engineer
Your boiler is struggling to read its internal temperature, so it has safely shut itself down to prevent it from getting too hot.
Full guide for E2003
E28 High Engineer
Your boiler has detected that the internal control computer installed is not the correct version intended for this specific model, preventing it from operating safely.
Full guide for E2804
E110 High Engineer
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.
Full guide for E11005
E125 High Engineer
Your boiler has detected that hot water is not flowing properly around your radiators or pipes, so it has shut down to prevent overheating.
Full guide for E12506
E133 High Engineer
Your boiler has stopped working because it cannot detect a flame or is not receiving a steady supply of gas.
Full guide for E133on the Baxi BBU 45/4
ThermocoupleGas ValveIgnition ElectrodeNTC Temperature SensorWiring HarnessPrinted Circuit Board (PCB)
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 Baxi 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