Main
Short Cycling / Oversized Boiler or Poor Control
Boiler frequently short cycles (turns on and off rapidly) during heating
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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 control settings, Blocked or undersized radiators, Faulty temperature sensor
How to Fix / Troubleshooting
Safety: Short cycling can reduce boiler life and efficiency but is not usually an immediate safety risk.
- Open all radiators: Ensure enough emitters are available to absorb the boiler output.
- Adjust room thermostat: Avoid setting the thermostat too high; use a stable setting to reduce rapid cycling.
- Check boiler output setting: Some Main boilers allow maximum CH output to be reduced via parameters; consult the manual or an engineer.
- Engineer tasks:
- Reconfigure boiler maximum CH output to better match the system.
- Verify correct operation of flow and return NTC sensors.
- Review system design and add radiators or buffer if necessary.
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Repair Difficulty
Medium
3/5
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