BoilerFaultCodesGlow-worm F.22 Fault Code
Also written as F22 — same fault.
The Glow-worm F.22 fault code means: your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.. It appears on 6 Glow-worm models in our database.
Technical description: Safety switch-off – low water pressure in boiler
What causes the Glow-worm F.22 fault?
This fault occurs when the water pressure inside your heating system drops below the minimum level required for the boiler to fire up safely. The most common reason is a slow leak from a radiator valve or pipework, though it can also happen if you have recently bled your radiators and haven't topped the pressure back up.
This fault often appears in autumn when homeowners turn their heating back on for the first time, as small leaks may have developed or radiators may have been bled during the summer break.
DIY fix possible
Locate the filling loop (a flexible silver hose) underneath or near the boiler.Slowly open the one or two taps on the hose until you hear water flowing.Watch the pressure gauge and close the taps once the needle reaches between 1.0 and 1.5 bar.
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Gas Safe Register →Glow-worm models that show the F.22 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F.22 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026