BoilerFaultCodesThe 6 most common faults
01
F.22 High DIY-safe
Your boiler has stopped working because the water pressure has dropped too low to operate safely.
What to try first
Locate the filling loop (usually two blue levers or a flexible silver hose) under the boiler.Open the valves slowly until you hear water entering and see the pressure gauge rise.Close both valves firmly when the gauge reaches 1.5 bar, then restart the boiler if necessary.
02
F.77 High DIY-safe
Your boiler has detected a blockage in the drainage pipe or the flue, preventing waste liquids or gases from escaping properly.
What to try first
Check the white plastic pipe leading outside to see if it is frozen or blocked.If frozen, gently pour warm (not boiling) water over the external pipe to thaw it.Clear any debris, such as leaves or nests, from around the flue terminal on your outside wall.
03
F.10 High Engineer
Your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water flowing to your radiators.
Full guide for F.1004
F.13 High Engineer
Your boiler has detected a wiring or sensor fault with the hot water supply, meaning it cannot safely monitor the temperature of your water.
Full guide for F.1305
F.25 High Engineer
Your boiler has shut down because the exhaust fumes are getting too hot, which is a safety measure to prevent damage to the internal components.
Full guide for F.2506
F.70 High Engineer
Your boiler's computer memory has been lost or corrupted, meaning the main control board no longer knows which model of boiler it is supposed to be operating.
Full guide for F.70on the Glow-worm 30cxi
Filling loopPressure sensorExpansion vesselCondensate trapCondensate pumpFlue pressure switch
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