High Lockout
E50 on Potterton Promax HE Store

Your boiler has detected a problem with the sensor that monitors the temperature of the exhaust gases, 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 NTC Fault

What causes this fault?

This fault occurs when the sensor responsible for monitoring the temperature of the exhaust gases sends an incorrect or missing signal to the boiler's control board. The most common reason is that the sensor has physically failed due to age, but it can also be caused by loose wiring connections or the boiler running too hot.

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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Related fault codes

E20View →E28View →

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