Worcester Bosch DHW Sensor / Flow Recognition Fault

Boiler displays A9, often with poor or no hot water delivery.

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

Incorrectly seated DHW sensor, Faulty DHW NTC, Faulty flow sensor, PCB logic fault

Safety first: Isolate power before any internal inspection.

Check hot water demand: Confirm that the boiler recognises a hot water demand (flame symbol or tap icon appears). If not, the flow sensor may be at fault.
Reset boiler: Perform a single reset and test hot water again.
Engineer tasks: A Gas Safe engineer should verify DHW NTC readings, check the flow sensor output, and replace the faulty component or PCB as necessary.

Hard 4/5

DHW Temperature Sensor (NTC)

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