BoilerFaultCodesYour boiler has detected a fault with a temperature sensor in part of your heating circuit, which likely means some radiators are not warming up as they should.
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
Technical description: Return sensor defective (zone 2)
What causes this fault?
This fault occurs when the boiler's control board loses communication with the temperature sensor responsible for monitoring water returning from a second heating zone. The most common reason is that the sensor has electronically failed or the electrical wiring connecting it to the main circuit board has become loose or damaged.
This fault is more common in autumn or winter when the heating is first switched on and multi-zone systems are put under constant demand.
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 712 — no call-out fees, no surprises.
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