E04
Hoval DHW Temperature Control Instability

Boiler shows E04, DHW temperature fluctuates, warning only

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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.

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Possible Causes

Partially blocked DHW plate heat exchanger, Faulty DHW NTC sensor, Rapidly varying flow rate at taps

How to Fix / Troubleshooting

Safety: Hot water can cause scalding. Use caution.

  • Stabilise flow: Avoid very low or rapidly changing tap flow rates. Open taps more fully to stabilise temperature.
  • Descale plate heat exchanger: In hard water areas, have a technician chemically descale or replace the DHW plate heat exchanger.
  • Check DHW sensor: Inspect and, if necessary, replace the DHW NTC sensor on the plate heat exchanger.
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Repair Difficulty

Medium 3/5

Required Part

DHW Plate Heat Exchanger
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