F25
FAULT CODE
Glow-worm
Circulation Fault (All Ranges)
Medium Severity
Engineer Required
On all Glow-worm boiler ranges, F25 (or F23) indicates a circulation fault — insufficient water flow through the primary circuit.
Step-by-Step Fix Guide
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Step 1
Check system pressure and bleed radiators
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Step 2
Ensure all valves are fully open
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Step 3
Reset the boiler
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Step 4 Engineer only
If fault persists, call a Gas Safe engineer to check the pump
Gas Safe Reminder
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.