BoilerFaultCodesThe 6 most common faults
01
E37 High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped too low.
What to try first
Locate the external filling loop, usually found underneath the boiler.Open the valves slowly to allow mains water into the system while watching the pressure gauge.Stop when the needle reaches the green zone, typically between 1.0 and 1.5 bar.Ensure both valves are fully closed and tight.
02
E 01 High Engineer
Your boiler is failing to start because it cannot light the internal flame needed to provide your heating and hot water.
Full guide for E 0103
E03 High Engineer
Your boiler has detected that it is running too hot and has automatically switched itself off to prevent any damage or safety issues.
Full guide for E0304
E26 High Engineer
Your boiler is trying to start but the flame is cutting out immediately, which means it cannot safely heat your water or home.
Full guide for E2605
E34 High Engineer
Your boiler is detecting that it isn't receiving enough electricity from your home to operate correctly.
Full guide for E3406
E35 High Engineer
Your boiler is struggling to detect a steady flow of electricity, which is likely caused by a minor power dip or a faulty electrical connection in your home.
Full guide for E35on the Keston C36p
Pressure relief valvePressure sensorExpansion vesselIgnition electrodeGas valveIgnition lead
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 Keston 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