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

Your boiler has shut down because it has either become too hot or detected that dangerous exhaust fumes are not escaping correctly through the chimney.

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

Overheat condition has occurred or Products Discharge Safety Device (TTB) has operated due to flue blockage.

What causes this fault?

This fault occurs when the boiler's internal temperature or flue gases exceed safe limits, triggering a safety shut-off to protect your home. The most common reasons are a failure in the pump preventing water from moving through the system or a blockage in the chimney preventing exhaust fumes from escaping.

This issue often arises during the first cold spell of autumn, when a pump that has been idle all summer fails to seize or move water correctly upon restart.

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
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