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Unstable Domestic Hot Water Temperature
Boiler runs but hot water temperature fluctuates or runs hot then cold at the taps.
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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 plate heat exchanger, Faulty DHW NTC sensor, Inconsistent cold water supply pressure, Sticking diverter valve
How to Fix / Troubleshooting
Safety: Water may become very hot unexpectedly; take care at taps and showers.
- Check flow rate: Fully open the hot tap and observe if the boiler maintains a stable flame. Very low flow can cause cycling; ensure any flow restrictors are not excessively limiting.
- Clean inlet filter: A blocked cold inlet filter can cause fluctuating flow. A qualified person can remove and clean it.
- Descale plate heat exchanger: In hard water areas, the plate heat exchanger may need descaling or replacement.
- Check DHW sensor: A faulty DHW NTC can misread temperature, causing overshoot and cycling. Replace if readings are unstable.
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Repair Difficulty
Hard
4/5
Required Part
Plate Heat Exchanger
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