Pentair
Short Cycling
Heater cycles on and off frequently without reaching the set 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
Low water flow causing high limit trips, Faulty temperature sensor reading incorrectly, Internal bypass or thermal regulator sticking, Oversized heater relative to system volume
How to Fix / Troubleshooting
Safety: Turn off power and pump before opening water-side components.
- Check and improve flow: Clean filter, baskets, and verify valves are fully open. Ensure variable-speed pump is set to a speed that meets heater’s minimum flow requirement.
- Monitor temperature readings: Compare heater’s displayed water temperature to an external thermometer. Replace sensors that are significantly inaccurate.
- Inspect internal bypass/thermal regulator: Remove header cover and check for sticking or scaled components. Clean or replace as needed.
- System design review: If the heater is significantly oversized for a small spa or system, consult a professional about flow balancing or control strategies to reduce cycling.
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Repair Difficulty
Medium
3/5
Required Part
Thermal Regulator
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