Danfoss Ally Short Cycling / Rapid On-Off Control

Thermostat frequently switches the boiler on and off in short cycles, causing noise and wear.

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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

Control cycle time set too short, Oversized boiler relative to system, Thermostat installed in draughty area, Incorrect control mode (PWM vs. on/off)

How to Fix / Troubleshooting

Safety first: No internal access required for most adjustments.

Steps:

  • Adjust control parameters: In the installer menu, increase the cycle time or select a more suitable control algorithm for your heating system.
  • Relocate thermostat: Move the thermostat away from draughts or direct heat sources that cause rapid temperature fluctuations.
  • Check boiler settings: Some boilers have anti‑cycling settings; adjust these according to the boiler manual.
  • Consult professional: If short cycling persists, a heating engineer should review system sizing and control strategy.
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Repair Difficulty

Medium 3/5
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