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

Your boiler has detected potentially dangerous exhaust fumes backing up into your home due to a blocked or obstructed chimney or flue, and has safely shut itself off to prevent carbon monoxide poisoning.

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

Products Discharge Safety Device (TTB) - CFL Only: In the case of flue blockage this device will operate and the boiler will go to lockout. Repeated shutdown should be investigated.

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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