Jandy LXi Not Enough Heat: Low Heat Output Troubleshooting

What Causes Low Heat Output

The LXi may fire normally without fault codes but not produce enough heat. This can be caused by the heater under-firing (not burning at full capacity), excessive heat loss from the pool, or an undersized heater for the application.

Step-by-Step Troubleshooting

Owner-Level Checks

Verify the heater is actually running

1. Check the controller is set to POOL or SPA mode with the set point above current water temperature.
2. When firing, the right LED should light RED. If not, the heater is not calling for heat.
3. If using AquaLink RS automation, confirm it is sending a heat call.

Check for heat loss factors

1. Is the pool covered? An uncovered pool loses heat rapidly, especially overnight or in wind.
2. Are water features running while heating? They dramatically increase evaporative heat loss.
3. Has weather been unusually cold or windy?

Tech-Level Checks

Measure gas pressures

1. Check manifold pressure with heater firing: NG should be 2.5″ WC, LP should be 9.0″ WC.
2. Low manifold pressure means the heater is under-firing. Check inlet supply pressure (NG: 5.0–10.5″ WC, LP: 11.0–14.0″ WC).
3. If supply pressure is low, the gas meter may be too small or the gas line undersized. Refer to the gas pipe sizing table in Section 4.1 of the manual.

Perform a temperature rise test

1. Measure water temperature at the return header before and during heater operation.
2. LXi 250 should produce 8–12°F rise. LXi 400 should produce 14–21°F rise.
3. If temperature rise is below minimum, the heater is under-firing. Check gas supply and manifold pressure.

Verify heater sizing

1. Consult your dealer or Jandy technical support to verify your heater is properly sized for your pool volume and climate.
2. If undersized, the heater runs continuously but never reaches set point.

Common Parts That Fix This Problem

• Gas orifices (if converted between gas types incorrectly)
• Gas valve/regulator (if manifold pressure cannot reach spec)
• Gas line upsizing (if supply pipe is too small)

How to Prevent Low Heat Output

• Use a pool cover to reduce heat loss by up to 70%.
• Verify gas pressures annually during pre-season startup.
• Turn off water features while actively heating.
• Run the pump continuously when heating a cold pool (set time clock for 23 hours).