The furnace indicates a domestic hot water sensor fault (on combi-style furnace/boiler units); hot water is unstable or unavailable.

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

Failed DHW NTC sensor on the plate heat exchanger, loose sensor connection, scale build-up causing incorrect readings, PCB sensor input fault.

Safety: Isolate the power and allow hot water components to cool.

Locate DHW NTC: On Baxi combi units, the DHW NTC is usually clipped into the domestic hot water outlet or plate heat exchanger.
Check wiring: Inspect the sensor connector and cable for damage. Reseat the plug.
Test sensor: Measure resistance at ambient temperature and compare it with Baxi's chart. Replace the NTC if readings are out of range.
Descale if needed: Heavy limescale on the plate heat exchanger can cause temperature instability. A professional can chemically descale or replace the plate heat exchanger.

Medium 3/5

DHW NTC Temperature Sensor

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