BoilerFaultCodesGlow-worm F0 Fault Code
The Glow-worm F0 fault code means: your boiler has stopped working because the water pressure is too low for the system to run safely.. It appears on 2 Glow-worm models in our database.
Technical description: Insufficient water pressure in the system (less than 0.5 bar)
What causes the Glow-worm F0 fault?
This fault occurs when the water level inside your central heating system drops too low for the boiler to operate safely. The most common reasons are a slow leak from a radiator valve or pipework, or the air being manually bled from radiators without the pressure being topped back up.
This code is particularly common in autumn when homeowners first turn their heating back on after summer, causing old seals to weep or revealing pressures that have slowly dropped during months of inactivity.
DIY fix possible
Locate the filling loop (usually a silver flexible hose) underneath the boiler.Slowly open the one or two taps/levers on the filling loop to allow water into the system.Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps fully.
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Glow-worm models that show the F0 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F0 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 7 July 2026