De Dietrich Temperature Instability / Short Cycling

Hot water temperature fluctuates, alternating between hot and cold during 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

Partially blocked plate heat exchanger on De Dietrich combi, Incorrect minimum flow rate at tap, Faulty DHW flow sensor, Oversized or undersized gas rate

How to Fix / Troubleshooting

Safety first: Avoid sudden temperature changes that can cause scalding.

Step-by-step checks:

  • Run a single tap fully open: Test with one hot tap fully open. Many modulating heaters require a minimum flow to regulate properly.
  • Clean inlet filters: Ensure cold inlet and system filters are clean to maintain stable flow.
  • Check shower mixer: Thermostatic shower mixers can cause fluctuations if faulty. Test hot water at a simple basin tap to isolate the issue.

When to call a professional: If fluctuations persist at all outlets, the plate heat exchanger or flow sensor may need service.

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Repair Difficulty

Medium 3/5

Required Part

DHW Flow Sensor
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