High
F1 on Viessmann Vitodens 100-W WB1B

Your boiler has switched itself off because the waste gases exiting the flue are dangerously hot, which usually indicates the internal heat exchanger is blocked or failing.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Max. flue gas temperature exceeded

From this model's manual
Verified against the Viessmann Vitodens 100 W Wb1b System installation & service manual, page 34.
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 high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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