Medium Lockout
80:0 on Viessmann Vitodens 300-W

Your boiler has detected a communication error with its internal control system or a connected sensor, which might cause it to operate incorrectly or stop working.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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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

Without time delay

What causes this fault?

This fault occurs when the boiler's central brain loses contact with the sensors that monitor heat levels, often due to a broken internal wire or a sensor that has failed completely. Because the control system can no longer safely tell how hot the water is, it shuts down to prevent the system from overheating. It is usually caused by a physical break in the electrical circuit or moisture damage to the sensitive electronic connections.

DIY fix possible

Turn the boiler power switch offWait for 60 secondsTurn the boiler back on to see if the fault clears

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Related fault codes

81:0View →88:0View →

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