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The Most Common Swimming Pool Heater Problems

Installing and troubleshooting a heater that is still under warranty without proper licensing can forfeit your warranty under the manufacturer’s terms and conditions. If your heater is out of warranty, sometimes, it’s simply cheaper to do it yourself. If you yourself in this scenario, this blog article is for you. In this blog article, we cover the most common swimming pool heater problems a pool owner might encounter and remedies to fix the issue.

My Heater Won’t Ignite

One of the most common problems with pool heaters is it failing to ignite.

Is your heater turned ON and the temperature set correctly?

  • Ensure that the thermostat is set to a higher temperature than the current water temperature.

Is your pump running with a clean filter and basket?

  • Inspect the pump and filter and clean if necessary.

Make sure that the pilot is lit (millivolt heaters).

  • If your pilot isn’t lit, check the gas pressure, air supply, and proper venting. Make sure the pilot tube is intact and not clogged. For MV heaters, if the pilot won’t stay lit, check the output on the thermocouple.

Is the gas supply valve in the ON position?

  • Without gas, the heater won’t operate. If the supply valve is OFF, turn it ON.

Are the plumbing and filter valves open?

  • Make sure to keep your valves open as to not prevent the water flow.

Low Water Flow

In order for a heater to operate smoothly and efficiently, it’s important that pool system maintains a consistent flow of water. Manufacturers equip swimming pool heaters with pressure sensors. These special sensors monitor and detect changes in water flow. For example, in some cases, you will see a “Low Water Flow” warning pop up on your heater’s LCD screen. Or, you might notice your heater isn’t pushing out as much warm water as it should or used to. Honestly, this is a very common occurrence. If you are experiencing low water flow, or your heater won’t start, ask yourself the following questions:

Have you cleaned your filter lately?

  • Monitor your PSI reading on your filter’s pressure gauge. If the PSI is too high, clean your filter.
  • Increasing pressure goes hand in hand with the decrease of water flow.

Is your pump basket dirty?

  • Check your pump’s strainer basket. Remove the basket and remove the debris with a hose.
  • Ensure the pump basket and lid are in good conditions. No cracks.

Do you have too many water features operating at once?

  • Your pool pump only moves a certain number of GPMs, therefore, too many water features can dramatically decrease your water flow.
  • If possible, replace the motor with a larger one.
  • Close water features, or alternate them, until the pool heats to the desired temperature.

Defective Pressure Sensor/switch (Most Common)

  • The purpose of the pressure switch is to ensure that water is flowing through the unit before it allows the heater to turn on.
  • The pool pump must be ON and your filter clean for the switch to close and allow voltage to pass through.
  • Test the voltage reading on the pressure switch with a multimeter.
  • Replace the pressure switch if necessary

Are you using the low settings on your variable speed pump?

  • For operation, heaters require a minimum GPM flow. If you are running your variable speed pump on the low setting, make sure you meet the minimum GPMs for your heater.

Pool Heater Turns ON and OFF (Cycles)

If your swimming pool heater is cycling ON and OFF, it is an early indication that the electrical connection or power supply is experiencing issues. However, it isn’t ALWAYS the case. There are other factors that can actively contribute to your heater’s ON and OFF cycles.

Is your pool water chemistry consistently and accurately balanced?

  • Poor water chemistry is one of the leading causes of equipment failure, especially pool heaters.
  • Test your water before adjusting your chemical levels. If unsure, please refer to the heater’s manual for the recommended chemical levels.

Have you inspected the pressure sensor, thermal regulator, and/or the high limit switch?

  • Inspect these parts for corrosion, scaling, and/or any electrolysis issues.
  • If the pressure sensor, thermal regulator, or high limit switch is faulty, corroded, or defective- replace it.

Have you cleaned your filter?

  • A dirty filter can cause low pressure and as a result, cause the heater’s pressure switch to turn OFF. A dirty filter can prevent a heater from firing and it can also cause your heater to shut off before warming the water to the desired temperature.

When’s the last time you have inspected and cleaned the heat exchanger?

  • Deterioration of the heat exchanger can impact your heater’s operation. Inspect your heat exchanger for chemical or sanitizer damage.

Pool Heater Isn’t Heating

Sometimes, your pool heater ignites but doesn’t reach the desired temperature. Or, maybe your heater isn’t generating heat at all. Both situations are very common.

Inspect your temperature sensor.

  • Make sure you have installed the temperature sensor correctly and it is in good condition.

Double check your thermostat settings

  • Set your thermostat to a higher temperature.

Did you properly size your pool heater?

  • If your heater is undersized, it will have problems heating your pool up. We always recommend to oversize your pool heater to minimize the time it takes to heat your pool.

author avatar
Charlie Ramirez
Writer at InyoPools.com, brings a wealth of knowledge and expertise in pool care and equipment, helping pool owners make informed decisions for over a decade.

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209 responses to “The Most Common Swimming Pool Heater Problems”

  1. Jamie Avatar

    Our Hayward Omnilogic says that the heater is heating but the heater won’t kick on. The pool temp is reading at 82 and the heater is set to 88. Any thoughts on what the issue could be?

  2. Rick Avatar

    Can I light my pilot light to test it before I turn on the pump and get water flowing through the pool heater. I have a Pintar Minimax 250. Older model…….probably around 20 years old.

  3. Kamy Avatar

    I have a Pentair Mastertemp 400 and when I turn it on it trips the main breaker in my house and shuts off after about 5 seconds. Could this be because of low flow?

    1. Matthew Simmons Avatar

      The Mastertemp has an alert or error code display on the control module. Have you had a chance to view it? If so, what code is it flashing?

      mastertemp error code flashes

  4. Scott Avatar

    I have a 20-year-old Hayward Swim Pro H150 pool heater. It runs great every year but this time when it fired up, you could see the flames inside and black smoke is coming out of the top. Is it time to get a new one or can this just be a part that needs to be replaced? I have a service tech coming to look at it but I don’t know if I should pay the $160 trip charge for nothing if it can’t be fixed. Thank you.

    1. Matthew Simmons Avatar

      The heater could just be dirty and in need of a thorough cleaning. If you are seeing black smoke, and the flame is not burning clean (the flame is orange, not blue) a dirty heater is my first hunch. I’d fork out the money for the service call.

  5. Mike H. Avatar

    Hello,

    I have a pentair Sta Rite 333 gas heater. It works great except it sounds like a subwoofer when it’s on. I can hear it from inside the house.

    Any ideas? It does heat the pool great otherwise.

    1. Matthew Simmons Avatar

      If you experience a rumbling/grumbling sound from the heater, you probably need to have the burner tray cleaned. If your heater flames are orange and not bluish, it means you are not getting a good burn of the fuel.

  6. mike g Avatar

    i have a hayward gas heater sw150 not heating the water at all everything is running fine getting gas water pressure all good no codes someone tells me it a bypass

  7. Dominic Avatar

    I have a Jandy Pool Heater, model LT400N-L (made 6-2006) and it stopped working. Red light on Pressure Switch. I put it on the to-do list for about 2 years. Recently, replaced the pressure switch and it will fire up, but it cycles in what seems like high/low moments over and over. Water is flowing, fan comes on, I see the flame in the tiny peep hole. Fan comes on 35 seconds, then a cycle of warm air comes out and fan gets louder for 15 seconds, then warm air ends and fan seems to drop a speed. During the warm air/ high fan cycles, the water does pump in hot into the spa. I have the Jandy PDA and the AquaLink RS cabinet–water temp registers spa=74 on the PDA and I have the temp set to reach target 102. The high limit switches are in excellent condition visibly but I still bypassed them with a jumper, no change. I found the diagnostic flow chart online, tested all the voltages, all was well until step 7=”After approximately 30 to 40 seconds of igniter heat up, is there 24 VAC at VAL terminal of the Ignition Control?” For as long as I kept the probe on that terminal, the brown wire (VAL) on the ignition control module measured 0. Could it be the ICM? Before I gamble on such an expensive part, can I bypass/jump/test this brown terminal, or do you see something else I’ve missed?

  8. Crystal Avatar

    We left our pool heater on last night and forgot to remove the pump timer switch so the pump turned off but the heater was still on. It had an error code of “low flow”. Now the heater ignites and runs but makes a low pitched whining noise andcthe water does not feel very warm out of the jets. Did we ruin our new 2019 jandy gas heater?

    1. Matthew Simmons Avatar

      Where the whining began after the heater fired dry; that could be scale that developed inside the exchanger while the heater ran with superheated water going through the exchanger. In this case, is the heater below the level of the pool, and if so, how many feet below? If the heater is located more than 5 feet below the body of water, then the atmospheric weight of the water is enough to close the contacts of the pressure switch allowing the heater to fire. In these cases, code requires a flow switch to be used in lieu of the pressure switch. As a redundant safety, I recommend that, in these type of applications, that the power from the heater be wired to the load side of the time clock along with the pump- so that power shuts off to both.

      Can you tell where the sound is coming from within the heater? Is it coming from the gas line, gas valve or the exchanger? There might be multiple problem areas.

  9. Chad Avatar

    Just purchased a new natural gas Hayward H350FD, also purchased a propane conversion kit to change it over. I got everything installed and the heater starts and fires up and the shuts off and gives a IF code. I checked when it was dark outside so i could see the flame glowing in the sight glass. Don’t know what to do now……?????

    1. Matthew Simmons Avatar

      My first thought/question, why didn’t you buy a propane heater to begin with? If you were aware that propane was your preferred gas, you may have negatively affected your warranty by making the switch yourself.

      I suggest you call a professional to come take a look if you are having any issues. This is a troubleshooting guide Hayward uses, but again, I suggest you call a professional.

      1. Chad Avatar

        Hey I do understand, but I got a big discount on the heater itself. Anyway, regarding the code, I believe that it is a gas line issue, I will be installing a new gas line and regulator and see of that helps.

  10. Wendy Avatar

    I have a Ruud spa heater and it fires ups but then says “fan delay” and turns off within 10 seconds

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