Herz DHW Temperature Instability

Hot water temperature fluctuates between hot and cold during use

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 Herz plate heat exchanger, faulty DHW NTC sensor, inconsistent gas supply, incorrect minimum modulation setting

Safety: Risk of scalding from sudden hot water surges.

Check flow rate: Avoid running multiple outlets simultaneously; Herz combi boilers have a maximum DHW flow rate.
Clean inlet filters: Clean the cold water inlet filter and any strainers to ensure stable flow.
Descale plate heat exchanger: Have a technician descale or replace the Herz plate heat exchanger if scale is suspected.
Verify sensor: Replace the DHW NTC sensor if readings are erratic.

Medium 3/5

Herz plate heat exchanger

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