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.
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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.
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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.
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206 thoughts on “The Most Common Swimming Pool Heater Problems

  1. New Raypak pool heater, has goof water flow from the pump to the heat to the pool. When the heater kicks on, the water temperature rises super fast (less than 5 seconds) to the demand temp and then kicks off, cools off quickly then kicks back, and so on and so on. What would cause the temperature to rise so fast like that?

    1. It doesn’t sound like you have enough water flow. How are you judging the strength of this water flow? Do you have a flowmeter? Are you sure you have the heater wired and plumbed in correctly?

  2. I have a Raypak gas heater. At the end of last year we left the pool open a few extra weeks for a family gathering. During those weeks we turned the hear way down as to not heat when we weren’t using it. The pilot was lit, but the heater wouldn’t fire. (Manual not electronic) I closed the pool. Now in spring I’m trying to get it to fire, but nothing. Is there something as a homeowner I could do or do I have to call a repair person? $3000 for a heater and now annual service calls? My previous heater lasted 20 years. Raypak, 20 weeks.

      1. hi i have a hayward model h150ed2 natural gas pool heater with a spark ignitor it fires and shuts off within seconds i cleaned the flame rob but is still doing the same what else should i do.

          1. From the manual: SF – Thermistor Error – An excessive temperature difference between the two thermistors (5 °F or more) or an “out of bounds” condition on both sensors (less than 10°F or greater than 180°F) will result in the error code. Automatic restart is 2 minutes after the error is corrected.

    1. I agree. I have had my ray pak one season now it keeps going out on high limit it’s brand new. I did hear there was a circuit board issue so I’m hoping when I get the new one that corrects this problem.

      1. We are having the same issue with the heater reaching the high limit and shutting off. Heater is one year old.

        1. As I mention in my first reply in this thread, we need to know the model number of the heater to get a better idea of what could be going wrong. If you would like a more accurate assessment, then we need more info.

      2. When heater ignites, sounds like it’s not getting flow or something is in it , load noises,like grinding sounds

          1. I have the same problem of grinding noise when running with no codes and I have a H150FDP

  3. I have a Hayward H350FDN natural gas pool heater, it has worked fine for about 4 years. The last time I tried to run it, won’t fire up. No error codes. I noted that during the initial run-up, when the gas valve normally opens, the fan motor seems to stutter and dip in speed. Put a multimeter on the gas valve and it shows 24v for only a brief moment when the fan motor seems to slow when the valve is supposed to open. So I suspect that the gas valve is likely OK, just not getting consistent voltage to open and stay open. Right now I suspect that the low-voltage transformer may be defective, but I’m curious if anyone else has seen these symptoms. Thanks.

  4. I have a Hayward H350 propane heater with IO code displayed. I have replace the ignitor but still have same problem and display. Was told maybe the control board was bad ?,any thoughts

    1. From the manual:

      IO – Igniter open error – If the control is not in lockout and senses that the igniter circuit is open when the blower is running the control will turn off the blower and go into lockout. Automatic restart 2 min after error is corrected.

      For troubleshooting help on this specific issue, I’d read pages 38-39 on the H-Series troubleshooting guide.

      1. I have a Haywood electric heater it starts then stops. And it says low pressure switch. Where is this switch located

  5. Hi all.

    I have a Hayward pool heater (model #H250FDN). Over the past week, the heater fired up and heated just fine. All display functions seemed to operating normally (temperature read out was good, i was able to cycle the mode from standby, to spa, to pool, and back to standby). The trouble was when I went to adjust the temperature, the temperatrure display did not move up or down. This weekend, when I finally had time to work on it, I see there is no power to the display at all: no service light, no heater light, no light or display of any kind. I checked the breaker and it is fine. The switch to the heater is on. I had a spare display board and swapped it with the same result.

    Any thoughts on what I can do to further troubleshoot?


    1. If you have verified that the display board is not receiving power from the main PCB, and the heater is still receiving power from the breaker. I would presume the main PCB is dead. Hayward’s troubleshooting process relies a lot on flashing error codes, but they aren’t much help when either of the boards is out.

    2. I have the same heater. The same thing is happening to me. My front display board doesn’t go on at all. Electric line is fine. Were you able to troubleshoot the problem??

    3. Hi Bob,
      I had this same problem. I had to purchase a new display board and cover (the part that we see). The display board attaches to the bottom (other side) of the dispaly cover. Once I replaced this I was able to see the lights again. Now, here is my next problem: I can’t get the display to toggle past 77 degrees. This is where my pool stops heating. My igniiton clicks, but then it fails to heat pas this point, sigh. I believe now it may be my thermostat. I’m going to work on this some more tomorrow. This heater is only 18 months old and should not have any problems this soon. I’ll keep you poste. I hope this helps.

        1. My MasterTemp 400 fails to work intermittently. All indicator lights go out and nothing I do makes them light up. Days later, they’re suddenly working again. Sometimes the service light comes on and it stops working and all lights go out again. Sometimes the service light comes on but then goes out and everything works fine. Do you think a new thermal regulator might be the answer?

          1. Is there a common thread between the times it does/doesn’t work? Has it just rained? Does it not restart after it’s been in heavy use? Does it not work on especially warm or cold days?

            Have you checked the circuit feeding the heater to make sure it is providing the proper voltage?

  6. I have a Hayward H100ID that will not ignite. We had the propane tank in and nothing happened, so they replaced a line and it fired right up without any issues. I ran it for a half hour and went to turn it on the next day and now nothing again. It clicks, but will not light. All connections have been tested by an electrician with no issues also. Please help! I’m so frustrated.

    1. I have a raypak 336A heater. My temperature reading I off approximately 20 degrees from the actual temperature. I replaced the temperature sensor and the circuit board. Neither fixed my problem. Other then the inaccurate temp the heater works fine

          1. Okay, Tony, I will ask the same question to you as well. Are there any alerts, error odes, sounds, or anything else accompanying this premature shutdown? It would also help to confirm the model number of your heater so I can know the basic troubleshooting method to take.

            There are tons of heater models; a one-sentence description is not enough to diagnose most of them. Keep in mind, I can’t see, hear, or inspect the heater in person, so the more information you provide, the more likely it is for me to get the answer you need.

    2. I’m sure the electrician did his best on the circuitry, but when dealing with a heater, you probably want to have an HVAC company take a look at the unit. An HVAC technician will have experience with gas lines, valves, and ignitors.

  7. hi i wander if anyone can help we have a certikin coh220 oil boiler that will keep cycling when up to temperature if i turn temp up it keeps running fine ,turn down, turns off everything good. just happens when gets to correct temperature.
    thanks for any help

  8. I have a Pentair Heater. Pentair Mastertemp Heater 460736 400K BTU Natural Gas. What is happening is we will use the heater to heat up the spa. The spa is about 500+ gallons of water. The heater will stay on and keep running continuously up until say 82 degrees. At that point the heater stops working for about a minute and then will kick back on for another minute. This goes on and on until the heater finally meets it’s set temperature. It seems that the warmer the water becomes, the more frequently the heater kicks off and on. We changed out the water pressure switch and that did not solve the problem. Pentair 470190 Water Pressure Switch Replacement Pool and Spa Heater. Any suggestions?

    1. Are there any diagnostic LEDs lit or flashing? That would help go a long way in finding the solution.

      My first guess is a thermistor or control module issue. But that is just a guess until I have the above info.

      1. There are no diagnostics LEDs that flash. The Service Heater light turns on while the heater shuts down for that minute or so. Then the Service Heater lights goes off as the heater kicks on again.

        1. Unfortunately, neither one of us have x-ray vision. You have to open up the heater to find where the leak is coming from. It could be a header gasket that is causing the leak. There could be a defect in the heat exchanger caused by the manufacturing process or imbalanced water chemistry.

          On-site inspection is the key to troubleshooting.

    2. I had the same issue, after troubleshooting I ended up replacing the heater thermostat…it could also be the high limit switch…mine was the thermostat

  9. I have a Zodiac Jandy pool heat pump, model EE3000T. It developed a fitting leak on the outlet side of the heat exchanger. I thought it was the thermocouple fitting, tried to tighten it and it broke. Removed it and plugged the fitting hole. Leak stopped. Heat pump will not run as LED panel says no water flow. Later located the water temperature sensor. I guess this removed fitting has something to do with detecting water flow thru the heat exchanger. Have not tried to jury rig a fix as I have the broken fitting. Any additional thoughts?

    1. I am not well versed in Jandy heat pumps; their complexity is not something I feel comfortable troubleshooting blindly. I suggest contacting the manufacturer to see if they will do a guided troubleshoot over the phone. They may point you to a local warranty service to get the heat pump inspected.

      1. Hi,
        I have a Hayward Titanium Heat pro model HP21104t model heat pump. Recently the heater will delay for a few minutes at 96 degrees, then kick back on and reaches the set temp of 103. Any idea why the delay in the heater? Thanks!

  10. Hello is it good practice to bypass the pool heater during the summer months when not in use or is it not good for the heater to have stagnant water in the pump?

  11. I have a Hayward H100ID. Everything works fine until after about 15 min, when the fan just blows cool air and there is no flame anymore. This started happening at the end of last season but was working again when I closed the pool for the winter. It has been working fine all spring until now. Again, I am experiencing the same issue from last fall. Any thoughts?

    1. Are there any other signs when the heater shuts down? How long after the flame goes out does the blower run? Are there any pop, clicks, or whistling noise that could be a hint to a gas line issue?

    2. LO – Water Pressure Switch, Vent Pressure Switch, or Temperature Limit Switch Fault

      This could be as simple as your filter was dirty, which constricted flow to the heater, or you would have to troubleshoot the various switches. If the LO code still pops up after cleaning the filter, refer to the below troubleshooting info:

      h100id lo troubleshooting
      h100id lo troubleshooting 2

  12. I have a Hayward pool heater and just replaced heat exchanger. All wire were put back as they were. The heater works the SHUTS off given a LO ERROR. I clean the filter. What can cause this. How do I check the pressure control

  13. Hello. I have a Hayward Easy Temp heater. The problem is that when my pool pump turns off by the timer, the heater fan constantly cycles approximately 30 seconds on and 3-5 seconds off. The compressor does not engage, just the fan. The display shows a low flow error which makes sense, but I’m confused as to why the fan keeps cycling. Thank you.

    1. Is the water to temp when the pump shuts off? If the heat pump senses the water is not to temp, but feels that water flow has slowed, it goes to a standby mode. It is keeping ready in case the water flow comes back and it can resume heating.

  14. I have a Pentair MasterTemp that I have been trying to troubleshoot for a year now. It calls for heat, heat starts for maybe 5-10 seconds, then stops, temp raises rapidly to 124 then slowly back down to 75 and cycles again doing the same thing over and over again. So far I have replaced the thermal regulator, igniter, thermistor and the bypass valve in the manifold.

    Today, I did a bunch of troubleshooting.

    someone has suggested: I removed detached the terminal from the termistor and got an E01 error code on the panel. I connected my old termistor and got a reading of 85 degrees. When I hold it, the temp slowly went up to 90. I then reconnected the terminal on the new terminstor and got 75 (I guess that’s the water temp).

    When problem started happening last early last year, one of the thing I did was replaced a broken Jandy check valve between the heater and chlorinator. I also noticed that the flap wasn’t opening even at 3450rpm and 20-25psi. Although, there’s strong water coming out of the 2 return lines. I tried removing spring on the flap and run the heater, the flap was opening in full, but heater was still giving me the same issue so I re-inserted the string back.

    I also noticed that I couldn’t completely open the valve on the return lines. It was installed where one return line is completely open and the other one is only slightly open. So, I opened the 3-port valve and adjusted it where the 2 return lines are fully open. I run the heater and this time it did something different. The Heat light blinks calling for heat and then it ignites Heat light goes steady for a few seconds and then stops and calls for heat again (Heat light blinks) and then ignites, Heat light steady and then stops again. It kept doing this several times and then sometimes the temp will start counting up rapidly and slowly counts down to the current temp and cycles again.

    Note: when the opened the manifold last winter to replace the bypass, the manifold and the heat coils have no signs of scales. Water has always been in tip top shape. I only found 1 small stone stuck inside where the bypass is. So I thought that was causing the problem. Water
    In case there is blockage in the heat exchanger, how do I fix that?

    Thanks for your advise.

    Here are the video links. 1st one is the initial issue. The 2nd is after modified the 3-port valve to the return lines.

  15. Pentair Master Temp 400. No service system or service heater lights. No codes lit on back of the board. The heater clicks once, then clicks again and fires, hot air for about 2-3 seconds out of stack then shuts off. Attempts to fire again. Same thing. Water flow is fine. Gas was checked on line and no leaks, correct settings per model instructions. What should I be looking for?

    1. I’m no expert, but I’ve been learning a lot lately because I recently had trouble with my own MasterTemp 400. Check the Thermal regulator. There’s a lot of videos out there about it. It’ll te you how to check and replace. Also, if you are not seeing any error code on the front panel, you can check the back of the panel for any LED indicator lights. There are also videos about this.

  16. I have a Raypak RP2100 heater. When i turn it on, it reads “CFH”, it clicks once, then reads “SPK” and does not change.

    1. Is the pilot lighting? If so, then the proving signal is not getting back to the PC Board. Confirm that all gas valve wiring is intact and connections are solid. Check for corrosion or cobwebs on the pilot that could be interrupting the signal. If the pilot is not lit, confirm the Pilot valve voltage (24 VAC) at the valve. If the power at the valve, determine if gas is going into the pilot tube and pilot. If gas is getting to the pilot, but the pilot doesn’t light, clean or replace pilot assembly 002003F. If there is no gas coming from the energized pilot valve, replace valve. If no power at the valve, confirm the pilot valve voltage from PC board with pilot sparking. If no power, replace the board. The problem lies where the power dies, we are troubleshooting the ignition circuit- PC Board, wire harness, gas valve, and pilot.

      Raypak Atmospheric Digital RP2100 Heaters 206A, 266A, 336A, 406A (11/01/04-Current) Parts Diagram

  17. I have a MasterTemp 200. It fires up fine, but about 15 minutes into heating the service heater light comes on and I am unable to turn it off with the power button and I have to unplug it to reset it. It fires up fine again then the same thing happens. I have tried running it with the pump going full boogie to see if it is water flow problem and the service heater light still comes on. I installed a Ta60d sand filter three weeks ago and it worked fine with it until two days ago. Advice?

  18. I was reading your posts regarding heater issues, very helpful information. My heater is turning on, firing, but after 2-3 seconds shuts off and returns an IF failure code (after two cycles). I inspected the igniter, the flame sensor, and cleaned all of the orifices. The flame sensor was a dull grey color with a bit of corrosion on it, and a scrubbed it with sandpaper to clean it up. The igniter has a bit of carbon build up but came off with my finger. Orifices were clean.
    I suspect maybe it’s the flame sensor? Any other suggestions?
    I had a pool guy out to look at it due to this issue a month ago. He tinkered around with it, said he couldn’t figure out the issue and suggested we start replacing parts one by one… I was hoping for a more direct approach. Then when he left the heater started working! So it’s been a month or more that it was running.

    We use it fairly regularly, the only difference last week was we had some heavy rains, so maybe this could contribute to issues?

    1. yes, my sprinklers hit the top of the hayward panel, putting some water in the exhaust and my heater won’t work for a day or two until it drys out..

  19. I have a Pentair mini max 100 heater hooked up to a cedar hot tub. The heater only comes on if it’s turned all the way up. I would appreciate any information to fix this problem.

  20. I have a Pentair Master Temp 300 Pool Heater that is 6 years old. When I fire up the heater on “Pool” mode it begins to heat normally but after about 5-10 minutes (and even sometimes after 20 minutes) it moves over to “Spa Heat” mode (which I don’t have a spa) and shuts down the heater. No code is present. I have replaced the Stack sensor thinking that it was the problem. Any ideas on what the problem could be?

  21. I have a H200 gas heater. It will turn on and turn back off after about 45 seconds. When it turns off it also turns the pilot flame off. it will kick back on when I get the pilot lit again but turns off again. Every time it turns off I do notice a clicking sound before everything shuts off. Any ideas?

  22. Hi, got a Hayward HP75TR, ’bout 3 years old now. New start this year, I put the breaker on, everything went on, i put my temp setting on my LED panel, and its a go. 2 hours later got a Error Code E08. Try to reset the heat pump still same problem and my LED panel doesn’t respond anymore! Might be a connection problem!! Is this is a common problem?? do i have to change my LED panel or the board itself inside?? Thank You!

    1. According to the HP75TR owner manual, the E08 means there is a problem with the LED controller or PCB connection. You need to check the connection of the NET and NET 1 cables. Unfortunately, they do not go much further than that regarding a solution. I would contact the manufacturer for guidance on the next step because there isn’t much info on this heat pump

  23. Hi,I have a Raypak 266 heater about 7 years old, everything is running fine. the pool place thinks it might be putting copper into my pool. Do I have to take it apart to check the heat exchanger ? how can I tell if its bad ? no leaking going on at all. Thanks a bunch

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