A temperature sensor is reading outside its expected range, so the boiler has flagged a sensor fault.
Most common on: Logic, Logic+, Vogue
C2 means one of the boiler's temperature sensors — usually the flow or return thermistor — is giving a reading the control board cannot make sense of, such as an open circuit, a short, or a value well outside the normal range. The board cannot trust its temperature readings, so it flags the fault.
It is most often the sensor itself or its wiring rather than anything mechanical. A reset can clear a one-off glitch, but a recurring C2 needs an engineer to test and usually replace the sensor.
Hold the reset button. If C2 clears and does not return, it may have been a transient glitch.
If the fault appears at a particular temperature or only when the heating runs, make a note — it helps the engineer pinpoint which sensor is at fault.
Testing and replacing a thermistor, and checking its wiring and the PCB, needs a Gas Safe engineer with a multimeter and the service manual — not a homeowner fix.
Work on the gas side of a boiler must be carried out by a Gas Safe registered engineer. The checks above are limited to safe, non-invasive things a homeowner can look at (pressure, resets, the gas supply) — if in doubt, stop and call an engineer.
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A temperature sensor is reading outside its expected range, so the boiler has flagged a sensor fault. C2 means one of the boiler's temperature sensors — usually the flow or return thermistor — is giving a reading the control board cannot make sense of, such as an open circuit, a short, or a value well outside the normal range. The board cannot trust its temperature readings, so it flags the fault.
You can try a single reset and the safe checks below, but Ideal C2 usually needs a Gas Safe registered engineer. Never work on the gas side of a boiler yourself — it is illegal and dangerous unless you are Gas Safe registered.
A recurring C2 means the underlying cause has not been fixed — most often faulty flow or return thermistor (ntc sensor). Resetting repeatedly will not solve it; get the boiler diagnosed properly.
See all Ideal fault codes.