Medium Warning
6C:100 on Viessmann Vitodens 050-W

Your boiler's internal pump for hot water is stuck running at full speed, which usually means there is a communication error or a part is beginning to fail.

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

Set speed internal DHW loading pump 100%

What causes this fault?

This fault occurs when the boiler's control board loses its ability to regulate the speed of the internal hot water pump, causing it to run at maximum power constantly. The most common reason is a communication failure between the pump and the main computer, often caused by a loose wiring connection or a failing electronic controller within the pump itself.

Engineer required

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

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