Boiler displays A09, domestic hot water temperature unstable or incorrect

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

Faulty DHW NTC sensor, Scale build-up around sensor pocket, Loose sensor connection, PCB sensor circuit fault

Safety: Isolate electrical supply and close cold water inlet if removing any wet components.

Technician steps:

Locate the DHW NTC sensor on the plate heat exchanger or DHW outlet manifold (depending on IVT model).
Inspect for scale or sludge around the sensor pocket; clean if necessary.
Check the connector and cable for damage or corrosion.
Measure the sensor resistance and compare with IVT charts; replace the DHW NTC if readings are incorrect.
If sensor is OK, test the PCB input and replace the control board if required.

Medium 3/5

DHW Temperature NTC Sensor

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