BoilerFaultCodesYour boiler has lost the ability to measure the temperature of your hot water cylinder because of a faulty sensor or a wiring issue, meaning it cannot heat your water correctly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Short circuit: Cylinder temperature sensor. NTC sensor defective, short circuit in the cable harness, cable/housing
What causes this fault?
This fault occurs when the electrical signal from the hot water temperature probe is interrupted, usually because the sensor has failed internally. The most common reason is that the sensor has developed a physical short circuit or the wiring connecting it to the main control board has become damaged or loose. Because the boiler can no longer tell how hot the water is, it stops heating the cylinder as a safety precaution.
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 F.12 — 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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