BoilerFaultCodesWhat the manual says
Manufacturer manualFlow and return sensors NTC 1 and NTC 2 reversed
What causes this fault?
This fault occurs when the boiler detects that the pipe meant to be getting hot is staying cool, while the return pipe is heating up instead. It is usually caused by the temperature sensors being clipped onto the wrong pipes during a repair or a fault in the internal wiring harness that confuses the control board.
This fault is most common immediately after summer maintenance or a parts replacement, as it usually stems from human error during reassembly.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Avoid the next call-out bill
A cover plan would handle faults like 424: no call-out fees, no surprise bills.
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