F.24 on a Glow-worm boiler means: temperature rising too fast. The boiler isn't seeing water move through it the way it expects — often because of low pressure, trapped air, closed valves or a pump problem.
This code applies to Glow-worm Energy, Ultimate, Betacom. Codes can mean different things on different models, so check the display against your boiler's user manual.
What you can safely check
- Look at the pressure gauge on the front of the boiler. With the heating off and the system cold, it should normally read 1 to 1.5 bar. Top up if it is low.
- Bleed radiators that are cold at the top to release trapped air.
- Make sure radiator valves are open, and if you have zone valves, that they are not stuck shut.
- Press reset once, following the instructions in your user manual.
When to call an engineer
If the code comes back, the pump may be stuck or failing, or there may be a blockage such as sludge in the system. A Gas Safe engineer can test the pump and check the circulation.
Never remove the boiler casing yourself — everything behind it must be handled by a Gas Safe registered engineer. If you smell gas, open windows, turn the gas off at the meter, and call the National Gas Emergency number on 0800 111 999.
Repair it, or replace it?
If your boiler is over 10 years old, compare a repair against a new combi before you pay for parts.
Applies to: Glow-worm Energy, Ultimate, Betacom
Meaning checked against: Glow-worm — fault finding codes (Energy range)
Last reviewed November 2026. Always follow your boiler's own user manual.