Emergency
370 on Viessmann Vitodens 100-W B1GA

Your boiler has detected a safety issue where the gas supply is failing to shut off correctly, causing the system to lock out for your protection.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

What the manual says

Manufacturer manual

Gas or modulation valve will not close

From this model's manual
Verified against the Viessmann Vitodens 100 W B1ga installation & service manual, page 59.
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 is a emergency severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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