Medium Lockout
79:1 on Viessmann Vitodens 300-W

Your boiler's electronic brains are experiencing a communication conflict or an internal memory error, which may cause the system to stop working correctly.

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

Control unit is fault manager

What causes this fault?

This fault occurs when the boiler's internal computer chips stop being able to talk to each other reliably across the main circuit board. It is usually caused by a physical degradation of the electronic soldering or a failure in the communication module that acts as the 'translator' for the system's instructions. When these signals are interrupted, the boiler shuts down because it can no longer safely coordinate the fan, pump, and burner.

DIY fix possible

Locate the power switch or fused spur for the boilerTurn the power off for 30 secondsTurn the power back on and wait for the system to reboot

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Related fault codes

79:0View →F4View →

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