High Lockout
E33 on Potterton Powermax HE

Your boiler has detected an issue with the sensor that monitors the temperature of the exhaust fumes, causing the system to shut down for safety.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Flue thermistor error

What causes this fault?

This fault occurs when the boiler's internal computer receives an incorrect or missing signal from the sensor that monitors the heat of the exhaust gases. It is usually caused by the sensor itself failing due to age, or a fault in the wiring that connects the sensor to the main control panel. Because the boiler cannot confirm that the exhaust fumes are at a safe temperature, it shuts down immediately to prevent heat damage.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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