Boiler indicates a DHW temperature control fault; hot water may be too hot or too cold.

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 in plate heat exchanger causing temperature spikes, Faulty modulating gas valve, Control PCB modulation fault

Safety: Risk of scalding from overheated water. Reduce DHW set temperature on the control panel and allow the boiler to cool before inspection.

Steps:

Verify DHW setpoint is reasonable (e.g. 50–55°C).
Check DHW NTC sensor mounting and wiring; replace if readings are unstable.
If hot water temperature surges or drops rapidly, the plate heat exchanger may be scaled and require descaling or replacement by a professional.

Gas valve and PCB modulation faults must be diagnosed by a Gas Safe engineer.

Hard 4/5

Plate Heat Exchanger

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