Termet Unstable DHW Temperature / Flow Modulation Issue

Hot water temperature fluctuates between hot and cold during shower use, without any error code.

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.

Possible Causes

Partially blocked plate heat exchanger on Termet combi boiler, Sticking three-way valve, Inadequate minimum flow rate through boiler, Faulty DHW NTC sensor or flow sensor

How to Fix / Troubleshooting

User checks:

Open the hot tap fully to ensure sufficient flow through the boiler.
Avoid mixing large amounts of cold water at the tap; adjust temperature at the boiler if possible.
Check that other hot water outlets are not being used simultaneously, reducing flow.

Technician checks:

Clean or replace the plate heat exchanger if scaled or partially blocked.
Verify correct operation of the three-way diverter valve in DHW mode.
Test the DHW NTC sensor and DHW flow sensor for correct readings.
Check gas valve modulation and combustion settings.

Stable DHW requires clean heat exchange surfaces and accurate sensing.

Repair Difficulty

Medium 3/5

Required Part

Plate Heat Exchanger

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