High Lockout
F.10 on Vaillant ecoMAX Pro 28E

Your boiler has stopped working because an internal temperature sensor has developed an electrical fault and is giving a false reading.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Flow NTC short circuit

What causes this fault?

This fault occurs when the sensor responsible for monitoring the temperature of the water leaving the boiler suffers an internal electrical failure. The most common reason is that the sensor has developed a short circuit, causing it to send an impossible reading to the control board, which shuts the system down for safety. Occassionally, this can also be caused by moisture ingress or a damaged wire leading to the sensor.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.00View →F.11View →F.20View →

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