Vaillant vSMART Short Cycling Due to Control or Sizing

System makes frequent short boiler cycles (on/off every few minutes) even when there is a steady heat demand.

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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 oversizing relative to system, minimum modulation not reached, incorrect vSMART control parameters, poor hydraulic balancing or low system volume

How to Fix / Troubleshooting

Steps to reduce short cycling:

  • Check flow temperature: In the app or boiler settings, reduce the maximum flow temperature to allow longer, gentler runs.
  • Enable weather compensation: If an outdoor sensor is installed, ensure weather compensation is active to modulate flow temperature.
  • Hydraulic balancing (pro): Have a heating engineer balance radiators and, if necessary, add a buffer or increase system volume.
  • Review boiler settings (pro): A technician can adjust minimum output and pump settings to better match the system.

Short cycling is primarily an efficiency and wear issue; addressing it improves comfort and boiler lifespan.

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Repair Difficulty

Hard 4/5
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