BoilerFaultCodesYour heat pump has stopped working because one of its outdoor temperature sensors is sending an incorrect or missing signal to the main control board.
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 board loses communication with the sensor that monitors the temperature of the coils outside. This usually happens because the sensor itself has failed internally or the electrical wiring has become corroded or loose over time. Without this specific data, the system cannot safely manage the heating process and shuts down to prevent damage.
This issue is more frequent during winter, as extreme cold and moisture can accelerate the degradation of exposed electrical sensors and wiring.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like E5 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
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.
Affiliate links — we may earn a commission at no extra cost to you.