BoilerFaultCodesThe 6 most common faults
01
23 High DIY-safe
Your boiler is struggling to push water around the system, likely because the water pressure has dropped too low or the pump is stuck.
What to try first
Check the pressure gauge on the front of the boiler; if it is below 1 bar, find the filling loop underneath the boiler.Open the filling loop valves to let water in until the needle reaches 1.5 bar, then close the valves tightly.Reset the boiler using the reset button on the control panel.
02
E119 High DIY-safe
Your boiler has stopped working because the water pressure inside the system has dropped too low.
What to try first
Locate the external filling loop, usually two silver flexible hoses with small valves underneath the boiler.Open the valves slowly to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves tightly to stop the flow once the correct pressure is reached.
03
20 High Engineer
Your boiler has stopped working because it cannot light the flame, which is sometimes caused by a blockage in the waste-water pipe.
Full guide for 2004
24 High Engineer
Your boiler has stopped working because it is unable to accurately measure the temperature of the water inside the system.
Full guide for 2405
25 High Engineer
Your boiler has stopped working because it is unable to accurately measure the temperature of the water inside the system.
Full guide for 2506
E20 High Engineer
Your boiler has stopped heating your home or water because it is failing to receive a proper temperature signal from its internal sensor.
Full guide for E20on the Main System 18 HE
Central Heating PumpPressure Relief ValvePressure SensorPressure relief valvePressure gaugeFilling loop
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