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.

Technical description

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.

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.

Find a Gas Safe engineer
Search the official register →

Related guides you might find useful

Boiler keeps losing pressure

Six most common causes of dropping pressure.

Read →

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →