BoilerFaultCodesGlow-worm F.24 Fault Code
Also written as F24 — same fault.
The Glow-worm F.24 fault code means: your boiler has shut down because the water inside is heating up much faster than it can be moved around the system, usually due to a blockage or a pump issue.. It appears on 6 Glow-worm models in our database.
Technical description: Safety switch-off – temperature rise too fast
What causes the Glow-worm F.24 fault?
This fault occurs when the heat exchanger gets too hot because the water isn't flowing away from it quickly enough. The most common reasons are a failing pump that can't push the water through or a build-up of sludge and debris blocking the internal pipework. In some cases, it can also be caused by air trapped in the system or a faulty sensor misreading the temperature.
This issue often comes to light when turning the heating back on for autumn, as pump components can seize up after being idle over the summer.
DIY fix possible
Ensure all radiator valves (TRVs) are fully openCheck that the boiler pressure is between 1.0 and 1.5 barPress the reset button once to see if the fault clears
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Glow-worm models that show the F.24 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F.24 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