Boiler shows A09, hot water temperature unstable or boiler shuts down intermittently

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Defective return NTC sensor, Damaged sensor cable, Loose plug on control board, Internal short due to moisture

Safety: Turn off power before removing covers.

Observe system behaviour: If the boiler cycles rapidly or shows unrealistic temperature readings, the return NTC may be faulty.
Reset the boiler: Try a reset to see if the error clears temporarily.
Visual check (competent person): Inspect the return NTC connection on the return pipe and at the PCB for secure fit and no visible damage.
Technician replacement: If A09 persists, a heating engineer should measure the NTC resistance and replace it if out of specification.

Medium 3/5

Return Temperature Sensor (NTC)

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