Junkers Unstable DHW temperature control

Domestic hot water temperature fluctuates between hot and 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

Partially blocked plate heat exchanger, Faulty DHW NTC sensor, Inadequate minimum flow rate, Modulating gas valve not adjusting correctly

Safety: Risk of scalding; be cautious when testing hot water.

Check flow rate: Open the hot tap fully; very low flow can cause cycling. Clean tap aerators and shower heads to improve flow.
Set temperature: Adjust the DHW temperature setting on the Junkers control to a moderate value (e.g., 50–55°C) and retest.
Technician actions:
- Clean or replace the plate heat exchanger if restricted by limescale.
- Test and replace the DHW NTC sensor if readings are unstable.
- Check gas valve modulation and burner pressure.

Medium 3/5

Plate Heat Exchanger

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