Applies To

All Intermatic pool and spa heat pumps.

Question / Problem

My heat pump is running, but the water temperature is not increasing. Why is this happening and what can I do?

Common Causes / Conditions

• The heat pump has not been running long enough to bring the water up to temperature, especially after a new installation or after being off for an extended period.
• Cool ambient air temperatures reduce heating capacity and require longer run times.
• Inadequate clearances or obstructions around the heat pump are restricting airflow and reducing efficiency.
• Insufficient or excessive water flow through the heat pump is preventing the water temperature from increasing as expected.
• Excessive heat loss from uncovered water surfaces or running water features is offsetting the heat being added.

Step-by-Step Resolution

1. Power Cycle the Heat Pump and Listen for the Compressor

   Turn the heat pump off, then turn it back on. The fan should run for about four to five minutes before the compressor engages and the red heating light turns on. If the compressor does not engage, or you hear a humming or buzzing sound when it tries to start, contact a qualified service technician.

2. Verify the Discharge Air Temperature

   Check the air coming from the top of the fan, or from the side fan on ECO550 and ECO900 heat pump models. The air leaving the heat pump should be about 9° F to 12° F cooler than the ambient air temperature. Cooler discharge air confirms the heat pump is transferring heat from the air to the water.

3. Confirm Normal Condensation

   After the heat pump has been running for a while with the compressor engaged, look for water or moisture around the base of the unit. This condensation is a normal byproduct of the heat transfer process and indicates proper operation. If you are unsure whether the water is condensation or a leak, turn the unit off and monitor the area.

4. Evaluate Daily Run Time

   In cooler weather, extend the run time of the pool pump so the heat pump can operate longer. For new installations or units that have been off for an extended time, allow the heat pump to run continuously for 24 to 48 hours to reach the desired water temperature. Heating time varies with pool or spa size and weather.

5. Optimize the Operating Schedule

   Schedule the heat pump to run during the warmest part of the day for best efficiency. Avoid running primarily late at night or early in the morning, when air temperatures are cooler and heat loss is greater.

6. Use a Solar Cover When Possible

   A solar cover greatly improves heating efficiency by reducing overnight heat loss. An uncovered pool can typically lose eight to 10° F overnight, while a covered pool may only lose about 3° F to 4° F. If a traditional solar cover is not practical, a liquid solar blanket can also help reduce heat loss.

7. Turn Off Water Features While Heating

   Turn off waterfalls, fountains, and other decorative water features during heating. These features increase the water's exposure to air and significantly increase heat loss.

8. Check Clearances and Airflow

   Verify the heat pump has adequate clearance on all sides and above. Remove any obstructions such as debris, furniture, or landscaping that might restrict airflow into or out of the unit.

9. Confirm Proper Water Flow

   Verify the water flow rate reaching the heat pump is within the recommended range, typically 50-60 GPM (gallons per minute) for most installations. Too little or too much water flow reduces heating efficiency and can lead to equipment damage. Consult a qualified pool professional if you are unsure how to measure or adjust water flow.

Tips / Additional Notes

• Heat pumps add heat gradually and perform best in moderate to warm ambient temperatures.
• Windy or cool conditions and large water volumes require extended run times to reach and maintain the desired water temperature.
• When the system is operating efficiently, the water temperature in the return line back to the pool will typically be about 3° F to 5° F warmer than the water entering the heat pump.
• If the water temperature does not improve after completing these steps, record the ambient air temperature, pool or spa water temperature, run schedule, and any error codes before contacting Intermatic Technical Support or a qualified service technician.