F20
FAULT CODE
Glow-worm
Safety Overheat Lockout
High Severity
Engineer Required
The safety thermostat has triggered due to overheating. Identical to Vaillant F.20 as Glow-worm uses the same platform.
Step-by-Step Fix Guide
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Step 1
Turn off the boiler and allow to cool for 30 minutes
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Step 2
Check and correct system pressure
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Step 3
Bleed radiators
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Step 4
Reset once
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Step 5 Engineer only
If fault returns, call a Gas Safe engineer
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.