BoilerFaultCodesGlow-worm F24 Fault Code
The Glow-worm F24 fault code means: your boiler is overheating because water isn't moving through the system fast enough, causing it to shut down to prevent damage.. It appears on 9 Glow-worm models in our database.
Technical description: Water temperature rising too quickly
What causes the Glow-worm F24 fault?
This fault occurs when the water inside the boiler heats up far too quickly, triggering a safety sensor to prevent the unit from melting or cracking. The most common reason is a blockage or a failed pump preventing the water from flowing out of the boiler and into your radiators. It can also be caused by a build-up of sludge or debris in the system that acts like a dam, trapping heat inside the heat exchanger.
This fault is most common when turning the heating on for the first time in autumn, as circulation pumps can seize up after being inactive all summer.
DIY fix possible
Check that all radiator valves are fully openEnsure your central heating bypass valve (if visible) is openTry resetting the boiler 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 F24 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F24 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