Dimplex Short Cycling / Oversized Boiler or Control Issue

Boiler cycles on and off rapidly, causing fluctuating radiator and hot water temperatures

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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

Boiler output too high for system load, Incorrect Dimplex control parameter settings, Faulty room thermostat with narrow differential, Blocked or undersized bypass causing poor flow

How to Fix / Troubleshooting

Safety first: Short cycling reduces efficiency but is not usually an immediate safety risk. However, it should be corrected to avoid premature wear.

User checks:

  • Thermostat placement: Ensure the Dimplex thermostat is not located near a heat source or in a draught.
  • Radiator valves: Avoid closing too many radiators; leave at least one radiator fully open to maintain flow.

Professional optimisation:

  • Adjust Dimplex boiler output and anti-cycling parameters in the installer menu.
  • Install or adjust an automatic bypass valve.
  • Consider upgrading to a modulating Dimplex controller if not already fitted.
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Repair Difficulty

Medium 3/5

Required Part

Dimplex automatic bypass valve (if fitted)
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