Heater Not Heating
Zodiac Jandy Pool Heater
Severity: ModerateWhat Does This Error Mean?
A Zodiac Jandy heater that runs but does not heat the water is usually caused by low water flow, an incorrect temperature setpoint, a dirty heat exchanger, or a failed high-limit sensor. Check the flow first — no heating is possible if water flow is insufficient.
Affected Models
- Jandy LXi Pool Heater
- Jandy Hi-E2 Heater
- Jandy JXi Heater
- Jandy Legacy LT Heater
Common Causes
- Temperature setpoint lower than current water temperature — heater sees no demand
- Low water flow preventing the flow switch from closing
- Dirty or scaled heat exchanger not transferring heat efficiently
- Tripped high-limit switch due to a previous overheat event
- Faulty water temperature sensor reporting incorrect temperature
- Undersized heater for pool volume and heat loss conditions
How to Fix It
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Check the temperature setpoint on the heater display.
The heater will not fire if the set temperature is equal to or below the current pool temperature. Set the desired temperature at least 2-3 degrees above the current water temperature and wait 10 minutes to see if the burner fires.
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Verify water flow is adequate.
The Jandy heater requires a minimum flow rate (typically 20-25 GPM depending on model) to close the internal flow switch and allow heating. Check that the pump is running, the filter is clean, and all valves are open. Low flow is the most common reason a Jandy heater runs but produces no heat.
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Check for a tripped high-limit switch.
If the heater overheated in a previous session, the manual high-limit switch may have tripped. Locate the reset button on the heater (check your model's manual for its location — typically inside the front access panel). Press to reset. If the high-limit trips again shortly after, there is an underlying overheat condition to diagnose.
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Inspect the heat exchanger for scale buildup.
In hard-water areas, calcium scale builds up on the inside of the heat exchanger over time, acting as insulation and dramatically reducing heating efficiency. Descaling requires a professional pool technician with acid flush equipment. If the heater is more than 5 years old and has never been descaled, this is likely contributing.
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Test the water temperature sensor.
A faulty temperature sensor can report that the water is already at setpoint when it is not. With an accurate thermometer, compare the actual pool temperature to what the heater display shows. A significant difference (more than 3-4 degrees) indicates a failing sensor.
Frequently Asked Questions
Why does my Jandy heater fire but the pool water stays cold?
If you can hear the burner firing but the water temperature is not rising, the most common causes are a severely scaled heat exchanger, very high heat loss (wind, cool ambient temperature), or the heater being undersized for the pool volume. A 400,000 BTU heater on a 25,000-gallon pool in cold windy conditions can take 24+ hours to raise the temperature significantly.
How long should a Jandy pool heater take to heat a pool?
As a rough guide, a 400,000 BTU heater raises pool temperature approximately 1 degree per hour per 10,000 gallons. For a 20,000-gallon pool, expect a rise of about 2 degrees per hour under normal conditions. Wind, shade, and a damaged or missing solar cover dramatically increase heat loss and slow this rate.