Emergency
Red LED illuminated (Lockout) on Potterton Kingfisher MF 40-100

Your boiler has detected that fumes are not escaping properly through the flue and has shut itself down for your safety.

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

Products Discharge Safety Device (TTB) - CF Only: In the case of flue blockage this device will operate and the boiler will go to lockout.

From this model's manual
Verified against the Potterton Boilerkingfisher Mf Rs40 100 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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