Emergency
Air flow rate safety device on Saunier Duval Thelia

Your boiler has detected that gases are not escaping properly through the flue, so it has safely shut itself down to prevent dangerous fumes 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 for any reason whatsoever, and causes reduction of the air flow rate, the built-in safety system of the boiler will be tripped: the burner will turn OFF and the fan will continue to run.

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