Dettson DHW Temperature Instability

Boiler short cycles on domestic hot water; hot water temperature fluctuates

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

Scaled plate heat exchanger, Faulty Dettson DHW sensor, Inadequate flow through DHW circuit, Mixing valve malfunction

Safety: Hot water can cause scalding. Use caution when testing taps.

Check DHW flow: Ensure that hot water taps provide a steady flow. Very low flow can cause cycling; clean faucet aerators and showerheads.
Inspect DHW sensor: Verify the Dettson DHW sensor is properly attached and wired.
Descale heat exchanger: In hard water areas, the DHW plate heat exchanger may need professional descaling or replacement.
Mixing valve: If a thermostatic mixing valve is installed, have it checked for proper operation and replaced if sticking.

Hard 4/5

Dettson DHW plate heat exchanger

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