Medium Lockout
71:2 on Viessmann Vitodens 200-W

Your boiler is having trouble heating your hot water cylinder because a sensor has detected an unusually high temperature or a fault during the heating process.

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

ON during DHW loading to set value 1

What causes this fault?

This fault occurs when the temperature sensor in your hot water cylinder detects a reading that is significantly higher than expected or rises too rapidly. This is often caused by a faulty sensor sending incorrect data to the boiler, or a mechanical failure like a stuck diverter valve preventing heat from moving correctly to your water tank. In some cases, it can also indicate a blockage in the heat exchanger that is causing the system to overheat locally.

Engineer required

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

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Related fault codes

F2View →A9View →

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