Emergency
Air flow rate safety device on Saunier Duval Sylva

Your boiler has detected that air cannot flow correctly through the exhaust flue, so it has safely shut itself down to prevent any harmful gases from building up.

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

If an obstruction, even partial, of the flue occurs, the built in safety system of the boiler will turn the boiler OFF and the fan will continue to run.

From this model's manual
Verified against the Saunier Duval Sylva 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 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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