Medium
A9 on Viessmann Vitodens 100 W WB1B 13kW Regular Boiler open vent

Your boiler is having trouble communicating with its external control panel or thermostat.

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.

What the manual says

Manufacturer manual

Communication Open Therm device fault

From this model's manual
Verified against the Viessmann/Viessmann Vitodens 100 W Wb1b Heat Only 5368662 installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

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

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Related fault codes

b5View →b6View →F2View →

All 23 fault codes on the Vitodens 100 W WB1B 13kW Regular Boiler open vent

Seeing a different code? Every code this model can display, in one place.

1018303850586068b0b8E5F0F1F2F3F4F8F9FAFCFdFF

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