Sime Inconsistent DHW Temperature

Domestic hot water temperature fluctuates between hot and cold during a shower on a Sime combi furnace.

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 DHW flow sensor, Modulation control issues, Inadequate minimum flow rate

Safety first: Turn off power and close water valves before removing DHW components.

Check flow rate: Ensure taps are opened sufficiently; very low flow may not keep the burner stable.
Clean inlet filters: Remove and clean any mesh filters on the cold water inlet to the Sime combi unit.
Inspect DHW sensor and wiring: Confirm the DHW NTC is secure and wiring is intact.
Descale plate heat exchanger (technician): A professional can chemically descale or replace the DHW plate heat exchanger if restricted by limescale.

Medium 3/5

Plate Heat Exchanger / DHW Flow Sensor

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