Medium Warning
b1 on Viessmann Vitodens 200-W

Your boiler's main control panel is having trouble talking to its own internal computer, meaning you cannot change settings or control the heating properly.

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

Control mode: Communication fault – programming unit (internal)

What causes this fault?

This fault occurs when the digital brain of the boiler loses its connection with the display screen you use to adjust settings. The most common reason is a loose internal wire or a component failure on the circuit board that prevents data from flowing between parts. It is essentially a communication breakdown inside the boiler's electronics that stops it from following your commands.

DIY fix possible

Locate the main power switch for the boiler (usually a fused spur on the wall).Turn the power off, wait for 60 seconds, and turn it back on to reboot the system.Ensure the control panel is pushed firmly into its housing if it is a removable type.

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