High Lockout
Ed on Ideal HP290

Your heat pump has stopped working because a sensor that monitors the temperature of the water returning to the outdoor unit has failed or detected an error.

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

Outdoor Unit, Return Thermistor (Tw_in) Error

What causes this fault?

This fault occurs when the heat pump's control system loses a reliable signal from the sensor that measures water temperature coming back from your radiators. This is usually caused by a physical failure of the internal sensor probe or a loose connection in the wiring that carries the data. Without this information, the unit shuts down to prevent itself from overheating or running inefficiently.

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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