F.05
FAULT CODE
Vaillant
Outside Temperature Sensor Break
Medium Severity
Engineer Required
The outdoor NTC temperature sensor cable is broken or disconnected. The boiler cannot read the external temperature for weather compensation.
Step-by-Step Fix Guide
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Step 1
Check if the outdoor sensor cable is visibly damaged or disconnected
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Step 2
Do not attempt to open the boiler or rewire the sensor yourself
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Step 3 Engineer only
Call a Gas Safe registered engineer to test and replace the outdoor NTC 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.