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.






70 thoughts on “The Most Common Swimming Pool Heater Problems

  1. Ok, I’m at my wits end. I read everything about D.E. going back into your pool. I have taken apart the Hayward 4820 filter over and over. There is no cracks in the standpipe, the o-ring is good on it. The manifold also has no cracks in it. I checked every grid for rips . The filter is running at 10psi with a clean startup and stays running that way. My return lines do not have the D.E. blowing out when I’m filtering for hours. The pool is clean. When the filter is off that’s when it seems the DE appears . I read there can be a suction leak. I do not have air bubbles. I replaced the gasket on the lid. I also opened the multiport and the spider gasket is in good condition. So why I’m I finding light grey D.E. in my pool everyday when I wake up. I will say my motor has been acting up and is ready to go!!! Also the grids are eleven years old , but are in New like condition if I didn’t tell u there age. Is there something I’m missing here?

    1. The only other thing I can think of is filter backflush. If your system loses prime when the pump shuts off, water inside the filter tank will go two ways, through the returns or backflush through the pump and out of the suction lines. I saw this phenomenon rear its head in a pool just the other day. We depressurized the system to install a salt chlorine generator, then when we started back up we noticed a heap of DE powder by the main drain.

  2. Ok, I have a new Hayward HP50TA Heat pump. Works fantastic. Very efficient and quiet. What I can’t figure out is how to get it to turn off when the pump turns off. When 5e pump stops on its timer, if the pool is not at the set temp, the heat pump shuts the fan off and goes into FLo mode (low water flow) mode, but does not shut off. Shouldn’t the heat pump power off when the pump is not running?

  3. My gas pool heater shut off because of no water flow. I have tried everything i can think of to get it to turn back on. I have tried flipping the breaker, checking all the connections in the heater. What do i do next?

  4. What would be a likely cause of a Raypak 266 gas pool heater to have close to a 10 degree (higher) difference than the pool water itself?

    1. Could be a bad temp sensor, or we have seen where the temp sensor rides upward and out of the sensor well. Usually, this occurs if there was water left to freeze in the bottom of the header, and the ice forces the sensor upward; then the sensor is reading cabinet temp rather than water temp.

  5. Hello,
    I was wondering if you could help me figure out what is happening to my heater. I have a Hayward heater and ProLogic unit that operates all equipment.
    Everything seems to be working fine, with the exception, that the heater is always ON. The ProLogic unit is set to Heater OFF, but the heater still turns on. Have you ever heard of this situation? Any ideas how to fix it?
    Thank you!

    1. I have the same set up, and I’ve come home on two separate occasions to the heater having turned on and the pool being over 97 degrees. I do not know why it is turning on. when I want to use the heater I have to physical press the buttons on the heater!

    2. I have the same problem, any help would be appreciated. I replaced the bezel and keyboard assembly as old unit was not working at all. Worn out my weather.

    3. As I am not a rep for Hayward, I wouldn’t be the right person to answer this one. But, it could be that the heater isn’t correctly wired to the pro logic or that isn’t properly set up in the settings of the pro logic.

  6. My Pentair 200 heater will turn on and red service light on immediately, the blower turns on, then the burner lights up runs for about 20 seconds and shuts off, blower cycles for about 60 seconds and shuts off, but board is frozen, no buttons on or off or temp control work unless I kill power, and I have done obvious filter cleaned, water flow good, gas is on, any suggestions

      1. Hi
        With the Hayward pro system panel is the heater set to pool or standby
        We just had the ignition switch changed but it said bo and was on standby
        I have switched it to pool. Is that correct ?

    1. Blow on the hose to the pressure switch and make it shift. Follow the rubber hose. One side is suction and the other is discharge. Either blow on the hose or suck on the suction side. It will manipulate it and force it to shift. If you don’t want to do that then you can always just jump it out. Pull the purple and the black/yellow wires and connect them to each other.

  7. Pool water was overheating. Was told thermostats
    were a common problem. Replaced both thermostats
    still have the same problem. (It’s an in ground, in Georgia, was fine last year. It was just filled to prep for season.)

    1. First, we need to know what type of heater it is. What is the model number of the heater? Knowing the make and model of a heater can narrow the possibilities of what is causing the issue.

  8. Water flow low. Compressor turns off. Cleaned system flow seems great. However fan motors run until compressor comes on. Within several minutes it shuts down. New filter new pressure gauge. Service indicated not low on Freon

  9. Hello, I have a a Hayward h250hdp… It was heating fine until today. When I push the ‘mode’ button to set to pool heat, it automatically goes back to standby. I’ve checked flow, gas, etc. Any ideas?

  10. Hi Matthew,

    My Raypak 266A popped the roll out fuse. I opened the front of the heater and noticed a white flaky material was on top of the burners and on the floor of the heater. I cleaned out about an 1/8th of a cup of this material. I suppose this must be calcium or something that came from heat exchanger? What do you think?

    1. Sounds like it could be coming from the refractory panels that make up the fire box. Is there any indication of pest infestation in the cabinet (on top of the heat exchanger, or in the junction box)? Had the heater been leaking or condensing? Moisture could cause the refractory to delaminate.

  11. Raypak 106a. Turns on and clicks for a while trying to light, but never does. Clicks constantly trying to light for several minutes. Flow switch is good. Sensors have continuity. High limit is good. Gas line is clear.

    Thinking motherboard or gas valve. Easiest way to diagnose this?

    1. Is the knob on the gas valve turned to ON? Was the air bled from the gas line?

      Check for 24volts at the pilot valve- red wire on gas valve. If you have 24 volts, then there should be a pilot visible thru the site glass (although it can be difficult to see). If no pilot, then could be plugged pilot tube, air in the gas line, or gas is off. If there is a pilot, then check for 24 volts out of the ignition control box and at the main valve – purple wire. If we have 24 volts out of the ignition control but not at the valve, then the wire or connections are bad. If we have 24 volts at the valve, then the valve could be bad or stuck. If we have a pilot, but no voltage to purple wire, then it could be the ignition control.

    2. Bleed air from the gas line, then look to see if the pilot is lighting. If no pilot, confirm that gas in turned on at the shutoff and on the gas valve in the heater. If still no pilot, check for 24v on the red wire leading to the gas valve. If we have 24v on the red wire, then the pilot valve should be open. Confirm by disconnecting the pilot tube from the gas valve- when the heater is sparking, there should be gas coming out of that hole. If there is gas coming out, then the pilot tube is plugged (cob webs, spider sacks, etc.) and needs to be blown out or cleaned. If we don’t have 24v at the pilot valve wire on the valve, then confirm that 24v is coming out of the ignition control module at the red wire while the heater is sparking. WARNING HIGH VOLTAGE: DO NOT TOUCH THE HIGH TENSION SPARK WIRE ON THE IGNTION CONTROL WITH POWER TO THE HEATER. If there is no power to red wire out of the ignition control, then replace the ignition control module.

      If there is a pilot, but heater doesn’t fire, then check all of the wires and connections leading from the gas valve to the ignition control module (particularly the ground wire) for missing insulation, heat damage, etc . If okay, then check for 24v at the purple wire leading the gas valve (with pilot lit). If we have 24v at the purple wire then the heater should fire. If not, still air in the gas line, or a bad valve.

      If we don’t have 24v at the purple wire, then check for 24v out of the ignition control module. If no power out, then the ignition control is bad.

      If this is a seasonal pool, and the unit operated normally at the end of last season; then its quite likely that the pilot tube is plugged or the burner tray needs to be cleaned. Hope that this helps.

  12. Rypak 185B turns on, ignites and burner seems to be working well. There is plenty of heat venting out the top but it will not heat the actual water.

  13. I have an old Jandy gas pool heater. Externally, it is in pristine condition because it’s located in my basement (not by choice, I bought the house that way).

    Very recently, the pool heater has been going on and off when the pool itself is OFF. It was happening again last night, and I had to turn the unit off manually. I then drained some water through the pressure relief valve that was literally hot enough to make tea.

    There is no backflow valve in the piping, but this unit has worked properly for the 9 years I’ve lived here. Any suggestions?

  14. Sorry, I should have provided complete unit information.

    It is a Jandy Lite 2
    Model #: LG175N
    Manufactured: April 2008

  15. I just had a brand new Hayward H150 Natural Gas heater installed…. it is intermittently kicking out the LO code while the pump is running. It’ll run fine for 30 minutes, shut down because of the LO error, kick back on, rinse and repeat throughout the time we’re trying to use the heater. Filter PSI reads 11PSI (normal post-backwash PSI is around 10). I’ve tried having just the skimmer valve open, then tried both skimmer and main drain open at the same time… same issue comes up. Hayward support hasn’t been particularly helpful. Would love your thoughts!

    1. Since it’s brand new, did you have the service company that installed it come back out to check the issue? Most new units experiencing a problem is usually an issue caused by the installation process. Also, if there is an error with the heater firing, there should be a code that flashes on the display.

  16. My raypak heater is throwing a roll back code at me three years old. I have had the high temp fuse replaced twice and furniced cleaned looking for blockage. None found. What next?.

    1. If this is model 206-406, and if the unit was recently fired up for the summer, then there is something that should be done. Spiders sometimes get into the burners and leave sacks behind. The sacks are round and sticky, so cannot be sucked or blown out. Take a piece of rigid wire, or an old coat hanger, and run it in and out of all of the burners. This can be done WITHOUT removing the burner tray itself. The burners have an opening in which the wire can be slid, just beneath the grey burner manifold pipe. This should only take 5-10 minutes and should be part of a spring cleaning routine. After running the wire in and out of all of the burners, fire the heater and examine the flame. There should be a well defined 4-5” blue flame with a little orange at the tips. If all else is good (adequate gas pressure, no soot buildup, etc.) then this should solve the rollout issue.

  17. I have a three year old Aqua Cal electric pool heater. Today the heater made a crazy loud noise the shut off completely. The outside circuit breaker for the heater tripped. When I flipped the circuit breaker back on nothing happened. The heater panel is still blank and pool heater stayed shut down . What could have occurred? This is puzzling me. I called my pool installer but they can’t come out for several weeks due to backlog of work.

    1. Heat pumps and specifically AquaCals are more intricate then I feel comfortable troubleshooting. Have you tried contacting get manufacturer for a troubleshoot? Or to see if they can light a fire under the local installer to get out there faster?

  18. I have a Rheem gas heater. It says Water temp 81 degrees. I have unit set to 90. It will fire up and run for 15 seconds and the temp says it goes to 90 and shuts off, then goes back to 81 in 30 seconds and repeats? Any idea

  19. I have a Sta-Rite Max-E-Therm 333 Model SR333NA. The water coming out of the returns is not nearly as hot as it was last season. I took the shell of the heater and blew/vacuumed out all the debris and it did not help much. Any suggestions or advice you can offer would be much appreciated!

  20. Heater Raypak P-R266A-EN-C, 266,000 BTU/HR, 10,000 GA in-ground pool. There is motorized vinyl pool cover. Heats up about 2 – 2.5 F / hr. Currently it’s 65F outside. The pool is now 77F. Is it normal heating speed? Any way to improve it by maintenance or adjusment? It ignites fine, no error codes.

  21. Hi,

    I have a Sta-Rite Sr400HD gas pool heater that is about 8 years old. It worked fine last season. This season it won’t fire up at all. I turn on the heater, green light is on pool and water temp says 73. there are no red lights. I raise the temp and the service system red light comes on. I took off the shell and vacuumed out all the debris. Took out my cartridge filters and cleaned them. Baskets are empty. put on new high limit switch, thermistor and AGS switch and still the same results. Any suggestions? Could it be the water pressure switch? I don’t have a voltmeter.


  22. I have a have a question on the Hayward h150fdp pool heater. Will heater go into standby mode when pump shuts down from timer?

  23. Have new Pentair Ultra temp 140.
    Keeps throwing the breaker at the Pentair panel after 1 hour of operation. Any thoughts as to why?

  24. Have a Hayward HeatPro HP21404T that is 4 years old. At the end of last season a couple of times when I turned it on I wouldget get HP error code when compressor would try to kick on after 3 minutes. It would reset then after 3 minutes it worked as normal. This year when I tried using it for the first time the breaker would trip every time the compressor would try to kick on. After HVAC tech authorized by Hayward opened it up he couldn’t find the problem but it went back to the HP error and then reset then it would work fine. Yesterday when I went to turn it off the display was not showing the temperature but was showing it was in pool mode and heating. Flow rate is 48 gpm through it. Is this a control board issue?

    1. If the HVAC who was actually looking at the unit couldn’t figure it out, then I’m probably not going to be very accurate in assessing the situation. Best guess would be a bad pressure sensor or a dirty filter. But the below is the manual explanation o the code:

      HP & HP3 – Low water flow to the unit or faulty high-pressure control. Check water flow. Backwash filter and/or heater. The unit will show HP3 after
      3 HP faults. This will stop your heater for protection.

      1. On the pressure sensor is the water in the tube supposed to go all the way to the switch? Mine stops short about 6 inches from reaching it.

  25. Matt- I bought a house with a smaller in-ground pool (approx 15′ x 30′, 3.5′ shallow, 5′ deep) that has a gas powered Raypak P-R206A-EN-C. Heater is 9 years old, worked great last summer- would heat the pool to temp in an hour or so, with very warm- almost hot- water pumped into the pool. This summer the heater fires up fine, plenty of heat coming from the unit, but water pumping in is luke-warm, and takes hours to get to 85, where it peaks out. The pool service company I inherited looked at it (unannounced while no one was home) and said the heater “couldn’t be working better” and that if I wanted more heat, they could install a bigger heater. This does not sound right… thoughts?

    1. A lot depends on what region in which the heater is located, as to the heat rise per hour. In the Midwest this year- without a cover- it has been difficult to achieve a decent heat rise- until a couple of days ago.

      Pool heaters do not modulate, they are either on or off- delivering a blended delta T of about 6- 8 degrees (inlet pipe to outlet pipe) no matter the pool or air temperature. I’m guessing that the service company confirmed that the heater was not shutting off intermittently and was running at a proper delta T. If so, then the heater is doing what it can do, though the water may feel different coming from the return- depending on the pool temp. A solar cover would help with heat loss, but that model heater is very capable of recovering heat loss in that size pool. Hope this helps.

  26. Hi Matt, any advice on my question from June 4 about the Jandy Lite 2 (Model #: LG175N)?

    Any advice greatly appreciated!


  27. Hello
    My Sta Rite SN0004NA heater turns on, fires up, heats water for 3 minutes and turns off. Then in 10 minutes it does it again.
    The filters are clean
    The pump basket is clean
    good water flow,
    had gas checked – that is fine.
    Any ideas?

  28. Just had my heater begin starting and stopping. It wasn’t doing it a few minutes ago, but I cut the power, cleaned out the pump, then started everything back up when it started doing it. It got a little splashed from the filter being open when I cut the pump back on. Any thoughts on what could be going on? Did the water from the filter possibly cause a short of some kind?

  29. My heater (pentair )is reading 94-96 degrees ( did read 104 earlier this afternoon but came down to 94 when I turned unit off then back on again) but is set at 80. To touch it is obviously not at 94. When I raised the temps to 95 the heater did click on. Can u tell me what the problem is.

  30. I have a Pentair Master temp 200 heater. The temp reading started fluctuating quickly from 81 to 85. The setpoint is 84. The heater burner kicks on and off following the temp fluctuations. I replaced the thermistor and cleaned the control board and connections. Same results. Is this a control board issue?

  31. Hi Matt
    I have a raypak PCO 430 gas heater. Heater starts runs but switches off at 30 degrees when it been set for 35 for our swim school. Heater was off for two weeks in our holiday period,
    Any help with solving this issue would be greatly appreciated. You are a knowledgeable guy.
    Cheers and thanks again

    1. When the heater is shutting off, is it giving a service code on the display? Could be shutting off due to low water flow to the heater “O”. Or if F2, F3, or F4 is coming up then it is a sensor problem. Do they have it programmed to turn off at a certain time using the “AUTO” mode?

  32. I have a Hayward h400idl and i first had a fire on the board, so i replaced it, then it wasn’t getting gas so i replaced the gas valve. Then i was getting the ao code, so i replaced the blower. It worked for one night on the hot tub, and then i got the ao code again. I sent it back, got a new one and new hoses and the blower vacuum switch and the vent pressure switch. I got ao code quick and i noticed the blower was really hot. The hoses looked like they moght be melting. Any ideas? TIA

  33. MiniMaxNT LNSeries. Pool pump on – it fires up fine within 15 seconds or so. Pool features off and pool return is on full. I have the heater set to 102 and it is starting at 60. It only heats up to about 62 after an hour. The water coming out of the spa return is just warm, not hot.

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