F66
FAULT CODE
Glow-worm
Frost Protection Active
Medium Severity
DIY Check Possible
The boiler is running in frost protection mode to prevent freezing.
Cold Weather Note
This is normal winter behaviour.
Step-by-Step Fix Guide
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Step 1
No action needed — the boiler is protecting itself and the system from frost
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.