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 4 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 internal sensors detect that the water level has dropped below the minimum safe operating limit. The most common reason is a slow leak from a radiator valve or joint, though pressure can also drop if you have recently bled your radiators without topping the system back up.
This issue is more frequent in autumn when homeowners turn their heating back on after the summer and discover pressure has gradually bled away over several months.
DIY fix possible
Locate the filling loop (usually a silver flexible hose) underneath or near the boiler.Slowly open the one or two taps/valves until you hear water entering the system.Watch the pressure gauge and close the taps firmly once the needle reaches 1.5 bar.
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Gas Safe Register →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 27 April 2026