BoilerFaultCodesGlow-worm F75 Fault Code
The Glow-worm F75 fault code means: your boiler is struggling to detect a rise in water pressure when the pump starts, which is preventing it from firing up to provide heating or hot water.. It appears on 9 Glow-worm models in our database.
Technical description: Pump / Water pressure sensor fault
What causes the Glow-worm F75 fault?
This fault occurs when the boiler's control board fails to detect a small surge in water pressure that should happen every time the internal pump starts up. The most common reason is that the pressure sensor has become blocked with sludge or has failed, but it can also be caused by a sticking pump or a loss of air in the expansion vessel. Because the boiler cannot confirm that water is moving through the system, it shuts down as a safety precaution to prevent overheating.
This fault is more frequent in autumn when the heating is turned back on after a long summer break, as the pump can seize or 'stick' due to several months of inactivity.
DIY fix possible
Check the pressure gauge on the boiler front or under the casing; it should be between 1.0 and 1.5 bar.If the pressure is too low, use the filling loop to top up the system until the gauge reaches the green zone.Press the reset button (indicated by a flame with a cross through it) to see if the boiler restarts.
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Gas Safe Register →Glow-worm models that show the F75 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F75 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