BoilerFaultCodesYour outdoor heat pump unit has detected a fault with a temperature sensor that monitors the air passing through it, which may cause the system to stop working correctly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Outdoor Unit, Air to Refrigerant Heat Exchanger Outlet Thermistor (T3) Error
What causes this fault?
This fault occurs when the heat pump's control system loses the ability to accurately read the temperature of the air as it leaves the outdoor unit. The most common reason is that the sensor has developed an internal electrical failure or the wiring connecting it to the main control board has become loose or damaged.
This fault can be more frequent during periods of heavy frost or high humidity, as ice build-up on the outdoor unit can sometimes physically stress the sensor or its wiring.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like 9.1.8 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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