Pentair Insufficient Heating / Underheating

Heater runs but water does not get warm or takes an extremely long time to heat.

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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

Incorrect thermostat setpoint, Oversized pool for heater BTU rating, Low gas pressure, Partially blocked burners or orifices

How to Fix / Troubleshooting

Safety: Turn off power and gas before inspecting combustion components.

  • Verify setpoint and mode: Ensure the heater is set to the correct mode (Pool/Spa) and the temperature setpoint is above current water temperature.
  • Check run time and expectations: Confirm that the heater BTU rating is appropriate for pool volume. Large pools can take many hours to heat.
  • Inspect burners: Look through the sight glass for even, blue flames across all burners. Uneven or weak flames may indicate dirty burners or low gas pressure.
  • Gas supply check: Have a licensed gas technician verify inlet and manifold gas pressures and correct any undersized piping or regulator issues.
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Repair Difficulty

Hard 4/5

Required Part

Burner Orifice Set
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