Thermona Inconsistent DHW Temperature Control

Domestic hot water temperature fluctuates between hot and cold during use.

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Safety Warning

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.

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Possible Causes

Scaled Thermona plate heat exchanger, Partially blocked DHW flow sensor, Faulty DHW NTC sensor, Inadequate gas supply or incorrect modulation

How to Fix / Troubleshooting

Safety: Risk of scalding from sudden hot water surges. Use caution when testing.

  • Check flow rate: Avoid running multiple hot taps simultaneously. Excessive flow can cause temperature swings.
  • Clean inlet filters (engineer level): Clean the DHW inlet filter and flow sensor turbine to ensure stable flow measurement.
  • Descale plate heat exchanger (engineer level): Remove and chemically descale the Thermona plate heat exchanger or replace it if heavily scaled.
  • Check DHW NTC: Test and replace the DHW temperature sensor if it gives erratic readings.
  • Gas rate check (engineer level): A technician should verify gas rate and burner modulation according to Thermona specifications.
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Repair Difficulty

Hard 4/5

Required Part

Plate Heat Exchanger
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