Viessmann Short Cycling / Oversized Boiler or Control Issue

Boiler frequently short cycles (turns on and off rapidly)

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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, incorrect minimum power setting, faulty room thermostat placement, lack of bypass or low-loss header

How to Fix / Troubleshooting

Safety: Short cycling reduces efficiency and lifespan but is not usually an immediate hazard.

  • Thermostat location: Ensure the room thermostat is not near heat sources or in direct sunlight.
  • Check TRVs: Avoid fitting TRVs in the room with the main thermostat, or keep them fully open.
  • Adjust settings (technician): A Viessmann-trained technician can reduce maximum output and adjust pump overrun and anti-cycling times in the service menu.
  • Hydraulic improvements: Consider adding a bypass valve or low-loss header if the system volume is small compared to boiler output.
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Repair Difficulty

Medium 3/5

Required Part

Room Thermostat
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