Defro
DHW Temperature Instability
Domestic hot water temperature fluctuates between hot and cold while a tap is running.
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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 Defro plate heat exchanger reducing heat transfer, Partially blocked DHW flow sensor turbine, Inadequate minimum flow rate through Defro boiler, Faulty modulating gas valve control
How to Fix / Troubleshooting
Safety: Water may suddenly become very hot. Use caution when testing taps or showers.
- Check flow rate: Ensure the hot tap is fully open. Very low flow can cause cycling. Avoid mixing with too much cold at the tap; instead, adjust boiler DHW setpoint if needed.
- Clean inlet filters: Clean the cold water inlet filter and DHW flow sensor turbine as described for E14.
- Descale plate exchanger: A technician can remove and chemically descale the Defro plate heat exchanger or replace it if heavily fouled.
- Gas modulation check: If the burner repeatedly ramps up and down, a professional should check gas valve modulation and combustion settings.
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Repair Difficulty
Medium
3/5
Required Part
Defro plate heat exchanger
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