Medium Lockout
F.13 on Vaillant ecoTEC Plus 836

Your boiler has detected an electrical fault with the sensor that monitors your hot water tank, meaning it cannot accurately tell if your water is hot enough.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Short circuit: Temperature sensor for the domestic hot water cylinder. NTC sensor defective, short circuit in the cable harness, cable/housing

What causes this fault?

This fault occurs when the electrical signal from your hot water tank’s temperature sensor is interrupted by a short circuit. The most common reason is that the sensor itself has failed internally or the wires connecting it to the boiler have become damaged or pinched, preventing the system from reading the water temperature.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.10View →F.11View →

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