Viessmann Unstable DHW Temperature Control

Hot water temperature fluctuates between hot and 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, inconsistent cold water pressure, partially blocked inlet filter

Safety: Sudden temperature changes can scald; be cautious when testing.

Check cold water pressure: Ensure stable mains pressure and that other taps are not causing large fluctuations.
Clean inlet filter: Many Viessmann combis have a cold inlet filter; isolate water, remove, and clean the mesh.
Replace DHW sensor: If the sensor gives erratic readings, replace with a genuine Viessmann NTC.
Descale plate heat exchanger (technician): Have a professional chemically descale or replace the DHW plate heat exchanger.

Medium 3/5

DHW Plate Heat Exchanger

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