F.11
FAULT CODE
Vaillant
Return NTC Short Circuit
High Severity
Engineer Required
The return temperature sensor has short-circuited. The boiler cannot monitor return water temperature and has locked out for safety.
Step-by-Step Fix Guide
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Step 1
Turn off the boiler
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Step 2 Engineer only
Contact a Gas Safe engineer to inspect wiring and replace the sensor
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.