High Lockout
20 on Potterton Promax Combi HE Plus

Your boiler has detected an internal sensor failure and has stopped providing hot water or heating to protect the system.

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

Temperature sensors faulty (DHW and CH sensors)

What causes this fault?

This fault occurs when the boiler's control board can no longer accurately read the temperature because the internal sensors have failed or become disconnected. Over time, these small probes can degrade due to constant heat cycles or moisture, leading them to provide incorrect signals that force the system to shut down for safety.

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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