Emergency
F.55 on Vaillant ecoTEC exclusive

Your boiler has detected an internal issue with its combustion monitoring system and has shut itself down to keep you safe.

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

The Live monitor shows S.40 and D.118 >= 1. The heat cell is in permanent comfort protection mode. Check and, if required, replace the all-gas sensor.

From this model's manual
Verified against the Vaillant Ecotec Exclusive installation & service manual, page 56.
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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