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Pool Heater Not Heating Water: Here’s Why and How to Fix It

Your pool heater may fail to heat water for multiple reasons, including a clogged filter, a wrongly set thermostat, an issue with the pilot light, poor ventilation, a faulty safety switch, or a power supply issue. Quick fix? Clean your device’s filters, check the thermostat’s settings, or investigate the power supply. The safest fix, however, is to seek assistance from a professional.

After ten years spent doing home repairs, one of the most common problems I get from pool owners is the pool heater not heating correctly. So if you’re facing this issue, you’re not alone. The first place to check is the heater’s filter to ensure it’s not clogged, and you need to check many other things. 

In this guide, I’ll discuss the most common reasons your pool heater is not heating water. I’ll also provide quick DIY fixes to try before contacting a professional.

Why Is My Heat Pump Not Heating The Water?

Here are some common reasons your heat pump does not heat water properly.

Clogged or dirty filter

The pool heater’s filter removes dirt and debris from the water that comes into the unit for heating. When the filter gets clogged or dirty, the water flow to the heater unit is obstructed, stopping the device from heating water properly. 

Clean your filter with high-pressure water or replace it to fix the issue.

Circulation pump run time

The job of the circulation pump is to distribute water and evenly spread heat throughout the pool. If your circulation pump doesn’t run long enough, your heater unit may be unable to heat the entire pool to the desired temperature. 

Check the circulation pump’s run time to ensure it runs long enough to assist the heater as it heats the pool.

Faulty safety switch or gas valve 

The gas valve in gas pool heaters controls the gas flow to the unit. A faulty gas valve could prevent gas from flowing to your heater, which can, as a result, affect water heating.

Electric pool heaters have a safety switch to keep the device safe in case of a hazard. The valve stops the heater when it detects a hazard. A faulty switch could halt the heater’s operation when it doesn’t need to. This will prevent your device from heating properly.

The thermostat is set poorly 

Check that your thermostat is correctly set. If the thermostat is below the minimum, your heater will not heat the water to the set temperature. 

The minimum thermostat setting on most pool heaters is 70 degrees Fahrenheit. However, the required thermostat setting varies depending on the heater and manufacturer. 

Check your manual for the correct value at which to set your thermostat. To fix this, adjust the thermostat to a higher setting.

Pilot light issue. 

The pilot light issue only exists with gas pool heaters. If you have an electric pool heater, skip to the next fix. 

The pilot light is responsible for igniting the main burner with gas pool heaters. When the pilot light fails, the burner will not be ignited, and your heater will not heat properly.

The pilot light often goes out because of low gas pressure or a pilot orifice. The pilot orifice is an opening in the pilot light assembly through which gas flows into the burner.

Check that your pilot light is ON. If not, here are the steps to relight a pilot light on a pool heater.

  • Turn off the gas supply.
  • Locate the pilot light.
  • Use a match or lighter to ignite the pilot light.
  • Turn on the gas supply to the pool heater.
  • Ensure the pilot light stays lit for a few minutes before you leave.

Closed plumbing valves 

Water gets into your heater through the plumbing valves. If these valves are closed, the water flow is restricted, and heating doesn’t happen. 

How to troubleshoot plumbing valves on pool heaters:

  • Inspect the valves for physical damage, such as leaks or cracks.
  • Turn the valves on and off. Ensure that the valves turn on and off and do not leak easily.

If you’re new to this, I recommend getting a professional plumber to do the inspection.

Lack of power source. 

If your pool heater is not plugged in or receiving enough power, it will not heat as it should. To resolve this, ensure that the unit is plugged in. Also, check that the circuit breaker is not tripped. Found a tripped circuit breaker? Reset it by flipping it to the “off” position and then back to the “ON” position. 

If the pool heater is still not working, have a technician check the connections.

Damaged wiring. 

Here’s how damaged wiring can cause serious problems for your pool heater:

  • Damaged wires can cause a short circuit, which can cause your heater to overheat and eventually receive permanent damage.
  • Damaged wires could trigger a fire if your device comes in contact with flammable material.
  • Finally, damaged wires will prevent your heater from heating properly.

To fix this, have a qualified technician replace the damaged wiring.

Poor ventilation. 

Ensure enough room around your heater unit for air to circulate freely. Remove any equipment or objects that could block your heater’s ventilation. 

How do I know if my pool heater is heating correctly?

There are a few indicators that your pool heater unit is heating correctly. Please check for these indicators before troubleshooting or calling for help.

Verify that the heating unit is running.

Verify that your pool heater unit has been running for at least four minutes and that the heating light is illuminated. It could take some time for the heating to begin. So wait at least four minutes to confirm that your unit is heating the water.

Feel air discharge from the top of the unit.

Place your hand over the top to feel the air discharged from your pool heater. Measure the temperature of this air with a thermometer to confirm that it’s cold. 

Expect the air discharged to be about 9 degrees colder than the ambient air temperature. If there’s cold air coming out the top of your unit, then heating will most likely occur. 

I do not recommend placing your hand in the water to feel the temperature change because the water returning to your pool may be slightly warmer.

Water from the base of the heater

If water flows out of the base of your heater unit, then it’s a good indication that there’s heating taking place. This flowing water is a result of condensation. The amount of condensation produced depends on the humidity, so don’t be surprised to find very little water.

If your pool heater is discharging cold air, producing enough condensation, and has the heating light illuminated, then it is most likely heating properly.

How can I heat my pool water faster?

Your pool heater can heat water faster if you do the following:

  1. Use a pool cover or blanket: A pool cover minimizes heat loss. Your pool’s temperature will increase quickly if your pool blanket is in place.
  2. Reduce water features: Water features use up more energy and will increase pool heating time. While heating the pool, reduce water features to a minimum or turn them completely off – to minimize energy use and heat the pool much faster.


Your pool heater won’t heat properly for several reasons, including a clogged valve, faulty safety switch or valve, lack of power supply, damaged wiring, poor ventilation, or a pilot light issue. In this guide, I’ve provided quick fixes – based on my experience – to help you get back to enjoying the warmth in your pool. I also recommend contacting a professional if you’re uncomfortable handling these devices.

Learn more about pool heaters and related hacks from our simple swimming pool guides.


  • Raoul Hayes

    Raoul Lobo is a seasoned expert in the realm of home appliances and environmental comfort. As a prominent author at, Raoul's passion and expertise shine through in his insightful articles and guides. With years of hands-on experience, he has become a trusted source for readers seeking advice on pools, washers, dryers, and a wide range of other appliances.

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