BoilerFaultCodesThe 3 most common faults
01
E4 High DIY-safe
Your boiler is having trouble moving water around the system properly before it fires up, often caused by trapped air or low pressure.
What to try first
Check the pressure gauge and top it up to 1.5 bar if it is too lowEnsure all radiator valves and isolation valves under the boiler are fully openGently bleed your radiators to remove any trapped air from the systemReset the boiler by turning the selector switch to 'R' for five seconds
02
135 High Engineer
Your boiler has stopped working because it cannot light the internal flame or maintain it, likely due to a gas supply issue.
Full guide for 13503
125 High Engineer
Your boiler has detected that the water inside the system isn't circulating or heating up correctly, preventing it from operating safely.
Full guide for 125on the Baxi Eco Compact
Circulating pumpFlow temperature sensorAutomatic air ventIgnition 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 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
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