BoilerFaultCodesThe 6 most common faults
01
F.22 High DIY-safe
Your boiler has stopped working because the water pressure inside your heating system has dropped too low.
What to try first
Locate the filling loop (a silver flexible hose) connected to the underside of your boiler or pipes nearby.Open the small valve or tap attached to the loop until you hear water entering the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone, usually between 1.0 and 1.5 bar, then tightly close the valve.
02
F.00 High Engineer
Your boiler has lost the connection to the sensor that measures how hot the water inside the system is, so it has shut down to prevent overheating.
Full guide for F.0003
F.75 High Engineer
Your boiler is struggling to push water around your heating system, likely because the internal pump is stuck, failing, or there is an issue with the sensor that detects water pressure.
Full guide for F.7504
F.01 High Engineer
Your boiler has lost the signal from one of its internal temperature sensors, meaning it cannot correctly measure the heat of the water returning to the system and has shut down as a precaution.
Full guide for F.0105
F.10 High Engineer
Your boiler has stopped working because it cannot correctly read the temperature of the water flowing through the system due to a faulty electrical sensor connection.
Full guide for F.1006
F.20 High Engineer
Your boiler has detected that it is getting too hot and has automatically switched itself off to prevent any damage or danger.
Full guide for F.20on the Glow-worm Compact
Filling loopPressure relief valveExpansion vesselFlow temperature sensor (NTC)Wiring harnessCentral heating pump
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 Glow-worm 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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