Medium
A9 on Viessmann Vitodens 100-W B1HC-19

Your boiler has lost communication with its smart thermostat or controller, meaning it cannot properly receive instructions to heat your home.

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

Control mode without Open-Therm device, Communication error, OpenTherm device, Check connections and cable; replace OpenTherm device if necessary.

From this model's manual
Verified against the Viessmann/Viessmann Vitodens 100 W B1hc B1kc 19 35 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

b4View →F4View →F5View →

All 29 fault codes on the Vitodens 100-W B1HC-19

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

0C5A101830385051525859A3b0b7b8E3E5F0F1F2F3F4F8F9FAFCFdFF

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