High Lockout
0A43 on Alpha Pro Tec Plus

Your boiler is currently unable to read the water temperature correctly because of a faulty internal sensor connection, which has caused it to stop heating your home as a safety precaution.

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

Return sensor short circuit.

What causes this fault?

This fault occurs when the boiler's internal computer detects a broken electrical signal from the sensor that monitors cooled water returning to the unit. The most common reason is that the sensor's internal components have failed or the wiring connecting it to the main control board has become damaged or loose.

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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