High Lockout
F.83 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler has detected that the temperature is not rising as expected when the burner is lit, which usually means there is a lack of water or a sensor issue.

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 and or return temperature sensor error

What causes this fault?

This fault occurs when the boiler fires up but the sensors don't detect a corresponding rise in temperature, leading the system to believe there is no water to heat. The most common reason is a low water level or air trapped in the system, though it can also be caused by sensors that have become unclipped or faulty.

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.22View →F.24View →F.73View →

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