Glow-worm · Current Glow-worm F-code boilers
F.22Low water pressure in the system
This code applies to Energy, Energy7, Ultimate3, Sustain, Betacom4. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Check the pressure gauge with the system cold.
- If it is below the range stated in the boiler manual, repressurise only by following that model's user instructions.
- Stop and book an engineer if pressure drops again, rises excessively, or there is a visible leak.
How an engineer may fix it
Check for leaks, trapped air, the pressure sensor, pump and expansion vessel; repair the underlying fault before recommissioning.
Glow-worm presents these as a general current-code guide; verify applicability in the exact appliance manual.
Manufacturer source: Glow-worm UK — Boiler Fault Codes. Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.