Vaillant Underheating DHW / Insufficient Output

Water heater’s hot water is not hot enough even at maximum setting

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

Gas supply pressure too low, Partially blocked burner or injectors, Scaled heat exchanger, Faulty DHW NTC over-reading temperature

Safety: Gas pressure and combustion checks must be done by a qualified gas engineer.

Check flow rate: Reduce the hot water flow at the tap to see if temperature increases. Excessive flow can exceed the heater’s capacity.
Descale heat exchanger: Remove and descale the DHW plate or primary heat exchanger.
Test DHW NTC: Replace if it over-reads, causing premature modulation down.
Check gas rate (engineer): Verify inlet pressure and burner rate. Clean burner and injectors if partially blocked.

Hard 4/5

Burner Assembly

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