High
F.104 on Viessmann Vitodens 222-F B2TF

Your boiler has received an 'alert' signal from an external part of your heating system, such as a smart thermostat or a safety accessory, which has told the boiler to stop running.

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

External fault message input active

From this model's manual
Verified against the Viessmann Vitodens 222 F B2tf installation & service manual, page 93.
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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Related fault codes

F.105View →F.108View →

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