Ruud Short Cycling / Control or Sizing Issue

Boiler short‑cycles (turns on and off frequently) without maintaining steady temperature

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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

Oversized boiler, incorrect control settings, faulty temperature sensor, inadequate system water volume

How to Fix / Troubleshooting

Safety first: Turn off power before adjusting internal controls.

  • Check thermostat settings: Ensure the thermostat is not set to an excessively tight differential or using an aggressive cycle rate.
  • Review boiler parameters: Using the Ruud control menu, verify minimum run time, differential, and outdoor reset settings are appropriate for the system.
  • Inspect sensors: Confirm supply and return sensors are properly attached and reading correctly. Replace any suspect sensors.
  • Hydraulic adjustments: In systems with very small water volume, adding a buffer tank or adjusting flow may be necessary. This should be evaluated by a heating professional.
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Repair Difficulty

Medium 3/5

Required Part

Supply and Return NTC Temperature Sensors
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