Emergency
Air flow rate safety device on Saunier Duval Thelia 23E

Your boiler has detected that it cannot safely push exhaust gases outside, so it has shut itself down to prevent a dangerous buildup of fumes in your home.

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/Saunier Duval Thelia 23e 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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Related fault codes

F1View →F4View →

All 20 fault codes on the Thelia 23E

Seeing a different code? Every code this model can display, in one place.

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