ATAG Unstable DHW Temperature Control

Hot water temperature fluctuates or runs hot then 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

Scaled plate heat exchanger, Faulty DHW NTC sensor, Inadequate flow rate through DHW heat exchanger, Modulation issues with gas valve

Safety first: Water can become very hot; take care when testing taps or showers.

Ensure the cold water inlet isolation valve is fully open to provide adequate flow.
Clean any inlet filters or strainers on the DHW side.
Descale the plate heat exchanger if limescale is suspected (common in hard water areas); this is usually a technician task.
Check that the DHW temperature setting on the ATAG controller is appropriate and not set excessively high.
If fluctuations persist, the DHW sensor or gas valve modulation should be checked by a professional.

Hard 4/5

ATAG plate heat exchanger

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