F24
Glow-worm
Low Water Content / Pump or Flow Fault
Boiler shows F24, rapid temperature rise then shutdown
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Airlock in boiler or pump, Pump not running or incorrectly wired, Blocked primary circuit, Closed isolation valves
How to Fix / Troubleshooting
Safety: Allow boiler to cool before working on pipework. Isolate power before touching electrical connections.
- Check pressure and top up: Ensure system pressure is adequate (around 1.2–1.5 bar cold).
- Bleed boiler and pump: Some Glow-worm models have manual air vents on the pump or heat exchanger. Carefully vent air with a cloth to catch water.
- Verify pump operation: On a heat demand, feel the pump body; it should vibrate slightly and get warm. If not, it may be stuck.
- Engineer tasks:
- Check electrical supply to the pump.
- Free or replace a seized circulation pump.
- Inspect for blockages in the primary circuit or heat exchanger.
Do not run the boiler with known circulation issues; overheating damage can occur.
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Repair Difficulty
Medium
3/5
Required Part
Circulation Pump
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