ACV Legionella Cycle Failure

Legionella protection cycle not completing or not reaching required temperature

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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

Insufficient burner output, Incorrect legionella setpoint on ACV controller, Faulty DHW sensor, Excessive heat losses in tank or pipework

How to Fix / Troubleshooting

Safety: Legionella control is critical for health. Follow local regulations.

  • 1. Verify settings: Check that the legionella cycle temperature and duration are set according to ACV and local guidelines (often ≥60°C for a defined period).
  • 2. Check burner performance: Ensure the burner reaches full output during the cycle and that no errors interrupt it.
  • 3. Sensor accuracy: Confirm that the DHW sensor reads correctly; replace if it under-reads and prevents reaching target temperature.
  • 4. Insulation: Improve insulation on the tank and primary pipework to reduce heat loss during the cycle.

If the system cannot reliably complete legionella cycles, consult an ACV specialist to review sizing and configuration.

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Repair Difficulty

Medium 3/5

Required Part

DHW Sensor / Control Settings
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