F64
FAULT CODE
Glow-worm
NTC Sensor Short Circuit / PCB Fault
High Severity
Engineer Required
A short circuit involving an NTC temperature sensor or an internal PCB fault. Shared across Vaillant Group boilers.
Step-by-Step Fix Guide
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Step 1
Turn off the boiler
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Step 2 Engineer only
Call a Gas Safe engineer to diagnose whether the fault is with a sensor or the PCB
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.