Ariston DHW Temperature Instability

Hot water temperature fluctuates between hot and cold during shower use

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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

Scaled DHW plate heat exchanger, Faulty DHW NTC sensor, Inadequate flow rate, Mixing valve or thermostatic shower issues

How to Fix / Troubleshooting

Safety: Risk of scalding; test water temperature carefully.

  • Check other taps: See if the problem occurs at multiple outlets. If only one shower is affected, the thermostatic shower valve may be faulty.
  • Adjust flow: Set a moderate, steady flow at the tap or shower. Very low flow can cause the boiler to cycle.
  • Descale plate heat exchanger: A scaled DHW plate heat exchanger restricts flow and causes temperature swings. Professional descaling or replacement is recommended.
  • Check DHW sensor: A faulty DHW NTC sensor can misread temperature. Replacement is a relatively simple job for an engineer.
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Repair Difficulty

Medium 3/5

Required Part

DHW Plate Heat Exchanger
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