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Why Isn’t My Swimming Pool Heat Pump Heating?

Every swimming pool heating system has its share of problems, and heat pumps are no exception: over the years, we at AquaCal have helped many customers solve their heat pump problems. If you notice that your heat pump is not heating your swimming pool, there are a few things you can do before hiring a heat pump professional to check it.

  1. Check that your heat pump is getting sufficient water flow. Without constant, sufficient water flow, your heat pump cannot transfer heat from the refrigerant to your swimming pool. Insufficient water flow will not only lengthen your heating time, but also cause damage to your heat pump’s internal components. To check your water flow, make sure the valves to your heat pump are completely open and that your filter is clean.
  2. Free your evaporator coil from all obstructions. Air-source heat pumps transfer heat from the air to your swimming pool. Without sufficient air inflow and outflow, your heat pump will heat less efficiently. An inefficient heat pump will not only heat your swimming pool more slowly, but also increase your electric bill. Remove all leaves, pine needles, twigs, and other objects from the top and sides of your heat pump.
  3. Check the air temperature. Again, air-source heat pumps transfer heat from the air to your swimming pool. They therefore depend on the air temperature. Because more heat is present in higher temperatures, a heat pump operates more efficiently in warmer air. Similarly, a heat pump operates less efficiently in cooler air and will need to run for a longer period of time in order to heat your swimming pool.
  4. Measure the air temperature difference (A(Delta)T). A(Delta)T is the temperature difference between the air entering your heat pump and the air exiting your heat pump. A(Delta)T should measure between 9° and 12°F (5° and 7°C). If it does, then your heat pump is operating normally, and your heating failure is most likely due to inadequate run time of the heat pump. Remember, your heat pump’s run time depends on your filtration pump’s operation.

If, after you have performed these checks, you still feel uncomfortable about your heat pump’s operation, contact your licensed heat pump professional. Do you have any questions about your heat pump’s operation? Leave a comment below or contact us directly at AquaCal. We would be happy to help you!

This Post Has 91 Comments

  1. Hello,

    My aquacal heater fan is not turning on. The compressor kicks but not the fan. There are also no error codes

    1. Hi Dan,
      The fan should come on immediately when you first start the heat pump. After 3 or 4 minutes, the compressor will start. If the compressor is running, but the fan is not on, the unit will cut off with a defrosting or FS code. It sounds like you need service. Please call us at 727-823-5642.

      AquaCal Tech Support

    1. Hi Neal,
      It sounds like your water temp sensor is not reading correctly and needs to be replaced.

      AquaCal Tech Support

    1. Good Afternoon Steve,
      Hope you are doing well.
      The most common cause of the HP5 error code is a slow down of water flow to the heat pump.
      You have enough water to activate the water pressure switch, but not enough to remove heat from the condenser.
      This builds up pressure in the refrigerant system until you get an HP message & the machine shuts down for a short period of time.
      When an HP signal happens 5 times in 1 hour, the machine brings up the HP5 lock out code.

      The first step to correct this is to shut off power to the heat pump for 5 minutes.
      Next, you need to make a basic check through you filtration system.
      Check the pump basket & skimmer basket for debris, check the filter to make sure it is clean, check any bypass valves to make sure
      they are in the right position and if you have a variable speed, make sure it is running at a high enough RPM level to give you at least
      30 gallons per minute (GPM).

      Once you turn the power back on, the heat pump should run normally.
      To be sure, you will need to watch the heat pump as it starts up & goes into the heating cycle.
      The fan will start first and then the compressor will kick in between 3-5 minutes.
      If the heating light comes on and the HP signal comes up within 5-10 seconds, then there is a refrigerant blockage & the unit needs service.
      If the heating light comes on and the HP signal comes up after 30 seconds or more, then you will need to keep adjusting water flow.
      If the heating light comes on and the HP signal does not come up, then you should be good to go.
      Robert Brown
      Aquacal/AutoPilot Tech Support

  2. Hi,

    I am really hoping someone can help me.

    I’m in the UK and have a TEBAS heat fan pump, which no one seems to know about over here.

    The heat pump is switched on and the fan is running but does not seem to be heating up the water at all. The temperature here in roughly 15c and sunny.

    I did have the guy who installed it come over today and have a look and he said all the pressure seems fine and filters clean etc.

    On the control pad on the heat pump there should be 3 small symbols (like 3 small dots) under the temperature reading,

     First symbol indicate the water flow:
     Second indicate the fan:
     Third indicate the compressor:

    They used to be visible and now all 3 have disappeared , which is why I think the heat punp is not heating up the water.

    Please see the link to my manual is anyone can take a look file:///C:/Users/New%20user/Downloads/Handbook-Tebas-Inverter-20.1-Angielska%20(2).pdf


    1. Good Day Steve,
      Hope you are doing well. While we at AquaCal are not fully versed in the inverter heater, they still work in mostly the same manner of our heat pumps.
      After the fan has been running for a few minutes, the air coming from the unit should be 10 degrees F cooler or more than the ambient air.
      Reading the manual, the heater appears to have a process of operations indicator for it to run. The 1st indicator is a Flow indicator showing the unit is receiving water flow.
      The second indicator is for the fan & when that is present the fan should be running. When the third indicator comes on that should indicate that the compressor is running & the cold air should be coming from the heater.
      i am assuming at this point that the fan is running with no indicators on the display & you are not getting any cold air out of the top.
      This can be caused by a fan relay that is stuck keeping the fan running & a water pressure switch that is not recognizing water flow so that the machine knows to start the compressor.
      However there are several other issues such as a microprocessor board failure or a faulty display that could be the fault.
      As i do not have access to technical data about the unit, I cannot offer further advice other than to start with the water pressure/flow switch & move up from there.
      Robert Brown
      AquaCal Tech Support

  3. My heater was heating my pool. Then when I went to check , it was off. Tried to set temp higher and I hear a click like the compressor want to turn on. The fan does not work either

      1. Outside temp was 71 yet my pool only got as high as 68. Pressure from filter seems fine. I did need to refill most of the pool with new water last week could that be a reason why temp is so low?

        1. Yes, if the water added was cooler than the actual pool temperature, then there would be heat loss. After you finish adding water, you should continue to heat the pool and the temperature should rebound. I hope this was helpful.

        1. Good Morning Mr. Rivera,
          Hope you are doing well. When the unit is running normally, you should have cold air blowing out the top of the unit. If you do not have cold air, then a service call may be needed. Please feel free to call us at 727-823-5642 so tat we can get you in the right direction.
          Robert Brown
          AquaCal Tech Support

  4. We are trying to start our heater but the code keeps coming up “ high water temp”. Tried resetting it and till says the same message.

    1. Hi Diane,
      OtA, Over Temperature Alarm, means the heat pump is a measuring a water temp of 110. It normally means the water temp sensor is not reading accurately and needs to be replaced. Please call us at 727-823-5642 and will be happy to assist you.


  5. Our Heatwave pool heater won’t heat. Fan runs and there is a “motor” that tries to kick on but won’t. It does this several times in a row. The red light is lite up for heater. Could you give me ideas on what to check? Thank you.

    1. Hi Tony,
      It sounds like the compressor is not starting. The issue could be something simple, like a run capacitor, or something more complicated. Please call our tech support line at 727-823-5642 and we would be happy to assist.


  6. Opening the pool from the past winter, the water temp is reading 103 so the heater is not coming on, the water temp is actually 57 deg.

    1. Hello Stephen,
      It sounds like there is an issue with the heat pump water temp sensor. Please call us at 727-823-5642 for a replacement part number or for local service center information.

  7. Hi, i have just installed an air source heat pump and bypass but cant get the refrigerant level to 20 bar +/-2
    Its 22-23 bar. I have the bypass off and flow and return set to about half, i have tried constant adjusting and the heater shuts down if the flow gets too low.

    1. Good Afternoon Mr. Ward,
      Hope you are doing well. The heat pump is most likely going off on high pressure in the refrigerant system due to a lack of water flow.
      Most of our heaters are looking to get a minumum of 30 GPM to make sure that enough heat is taken away from the heat exchanger. Having too little water flow can damage internal components. I would please ask you to contact our Tech Support Dept at 727-456-7411 for further troubleshooting.

  8. Old Aerotemp ATS15000A-A only heats in spa mode and I am unable to change temperature setting.
    Is there a way to unlock panel and restore control panel operation?

  9. My heatwave aquacal is giving a HP5 readout and not heating I believe it is a high pressure refrigerant issue but why does’nt it heat ?

    1. Hello John,

      The most common reason for an HP5 error message is insufficient water flow through the heat pump. Make sure your filter and baskets are clean, make sure the pool is filled half way up the skimmer, and make sure there are no valves in the wrong position diverting water away from the heat pump. After checking for good flow to the heat pump, power the unit down at the breaker and back up. This will clear the HP5 error message and the unit will start up again. If you continue to get the HP/HP5 error message, please call us at 727-823-5642.

  10. We used to have a Jandy PDA to use the pool functions (heat, lights, spa, etc) and once that broke we haven’t used any of those things because a new PDA is $300-$400 and we can’t afford that right now. It has been a couple of years without the heater (Heatwave) being turned on. Unfortunately, our deep end pool drain cover came off (dang neighbor kids!) and now we need to warm up the pool in order for the repair guy to get in and fix it. We do not want to wait for the weather to warm the pool because it is dangerous to not have the cover on the deep end drain…we’ve all read those stories. So, I went out with the manual and followed the instructions to heat the pool but the unit will not kick on. The display does light up so there is power to it but it won’t kick on. I tried with the pool pump on and off, waited the 5 mins, increased heat, etc. All the troubleshooting instructions followed and the fan will not turn on and heater will not heat. Any ideas I can try without calling a repair person would be great, thank you 🙂

    1. Hi Dear Valued Customer,
      If the Heat Pump was programmed to communicate with your PDA, it will not run because it is waiting to get the signal from the PDA. Please, refer to the owner’s manual under Setting Operating Controls or HEATER CONTROLS to disable the communication or to deprogram the Heat Pump; If you prefer, you can contact us at 727-823-5642 and we can walk you through that process.
      Thank You

  11. My pool light on the heater is on and the red heat light is not on. Is there anything that could be checked before I call a technician. Also the temperature on the heater is much higher than the actual pool water temp. Model AC125. Thanks for your time!

    1. Hi James,

      The heat pump will not turn on unless the desired temperature is set above the current heat pump water temperature. If the heat pump temperature is reading higher then actual, i.e. heat pump reads 100 degf and pool temp is actually 80 degf, the heat pump will only turn on if you set the desired temp above 100 degf. It sounds like the water temp sensor needs to be replaced. Please call us at 727-823-5642 if you have any questions.

      1. in response to last. My heat pump reads 90.1degf. I set the heater to 95 degf. The fan goes on, pool light is lit green, heat light will not go on and water is not coming out hot.

  12. I have an old AquaCal Tropical pool heater. It wouldn’t turn on so we replaced the capacitor, and it comes on. I don’t know how a pool heater is supposed to work and don’t know if it is working. it has 2 manual knobs one says flow, the other says defrost, between them is a toggle switch that selects either flow or defrost. The model # is half gone but what i have is T90 A-B. it sounds like the compressor is working but the fan isn’t coming on. Any help would be great.

      1. My Heatwave Aquacal pool heat pump runs, red heating light is on, but it does not appear to be heating…indicates water temp is 64°, outside air temp is 74°. Water flow and airflow good, could a bad capacitor be a possible cause to not heat?

  13. Hello David,
    It is possible the water temperature sensor is reading higher than actual and needs to be replaced, but this is unusual for a new unit. There is a process to calibrate the temp sensor reading, but this is only recommended for temperature differences of 3 DEGF or less. If you would like to discuss this further with our tech support team, please call us at 727-823-5642.

  14. Our pool heat pump is less than a month old. When first run, you could set the target temperature to, say, 90F and all was fine. However the past week or so, when the digital readout on the pump reaches 90 and the unit starts “coasting”, the pool water temperature is actually only 84 or 85. We tried compensating by setting a new high of 92 but the read-out/actual water temperature difference is still about 5 degrees Fahrenheit. It’s a brand new machine and we will of course have service come and take a look. But out of curiosity, what is happening and is this a common teething problem?

  15. I have Model 155AHDSBTJ. It has stopped working, and I have tried all of the troubleshooting tips. The display indicates OFF, and when I depress the mode button it will go to HEAT for about 5 seconds, and then flip back to OFF. Any suggestions?

    1. Hello Rollie,

      After making sure the mode button is in HEA mode, can you press the up arrow to adjust the desired temperature? The desired temperature also has an OFF position. If you would like to troubleshoot while you are in front of the heat pump, please call us at 727-823-5642.

  16. I have a heatwave Heater. The valve that holds the temperature sensor broke and the heater leaked. We replaced it and the leak is gone. The heater is on. Could are free from debris, there is colder air blowing from the top, the red heating light is on. The temperature reading on the display stays at 72 degrees and the pool has not heated. It has been on for 4 hours. What could the problem be?

    1. Hello Daniel,

      If the heat pump is working properly, there will be cold air blowing from the fan, typically 9 – 12 degf cooler than the ambient air. You should also see condensation forming under the unit. You will typically see .5 – 1 degf per hour in pool temperature rise while running the unit during the warmest part of the day, i.e. 60 degf or higher. If you would like to discuss this further, please call us a 727-823-5642 or email us your contact number to

  17. Our heat pump says the temp is 104 degrees and it defenitely isn’t even close. The water is actually really chilly. Does anyone know what might be causing this? There aren’t any error codes showing on the display.

    1. Hello Janice,

      Thank you for contacting us! For better help you we need a little bit more information abut the problem. Can you please contact us at 727.456.7431 and we are going to do our best to help!

  18. Hi my heat pump has been perfect for several years I just turned it on this year fan blows, compressor kicks on, but no heat at all. Air out the top is very cold and it seems like it should be working fine. All I've noticed is that very little condensation is coming off the unit, it usually pours out gallons the humidity is so high here in FL, and I don't think the top is blowing upwards as high as usual. There are no obstructions, any ideas you might have?

  19. My heat pump has stopped heating. (27days past 5 year warranty) A service man came and checked refrigerant and all seems well. Ambient temp is 70, pool is about 65. I remember when you could feel the outlets in pool and it was warm (guess 100?). It's now exiting heater about 75. Any ideas you could give me?

    1. Good afternoon Scott-

      The water ∆(delta) or the temperature difference between the pool water and the water coming out of the returns is 3-4 degrees maximum under ideal operating conditions. This means for every hour the unit is running, you can expect between ½ a degree to 1 degree of temperature rise in the pool water. For example you could expect a temperature rise of 3-4 degrees after appx 5 hours of run time.
      Please do not hesitate to contact us should you have any additional questions!

    1. Good morning Mr. Schultz and thank you for reaching out to us. Please contact our service department (” target=”_blank”>” target=”_blank”>( and they will try to diagnose the issue over the phone with you or schedule a service call for you to help you get your unit back up and running. If you need further assistance please email your contact information to

      Have a good day!

  20. My heat pump is getting close to 10 yrs old. In the past week it has been unable to keep the pool heated to our desired 83 degree temp. There has been an ice formation on one side of the heat pump.about 12 inches square. The nighttime temps have dropped to about 15 degrees, but daytime temps are still in the 28-30 degree range. I've turned the unit off for a few hours and got rid of the ice, however it appears ready to make more as it gets frosted up again. Any ideas as to what's going on and whether I should spend anything on a 10 yr old machine?

  21. Hi, My Dream heat pump model ESDAW 22KH 3PH, has decided not to play any more, switched it on this morning and it tripped the main rcd, Had a look at all the wiring and all ok, could it be the pump and how to test if possible, many thanks, John

    1. Good morning John-

      Please give us a call at 727.823.5642 to review your issue with you. You can also send your contact information to if you rather have someone contact you. We'll help have your dream heat pump up and running as soon as possible! 🙂

  22. Heating unit (Heatwave SuperQuiet – R410A) currently runs, but has recently been shutting down, showing a FS code (outside air temp low) and failing to run. This may be normal and perhaps I simply haven't ever taken notice, hence the reason for the question. It does eventually kicks on by itself. I have also tried cutting the power source and restarting to get the code to reset and start the unit again. What I find odd and leads me to believe I have an issue is when it has occurred, the unit is cooler toward the bottom and there is visible condensation. In each case the outside temperature has never been below 70 degrees Fahrenheit and I do not set the temp on the unit higher than 86. I live in PA and I have noticed the error code over the course of the last 2 weeks. There is a medium sized holly bush near the unit to act as a visual barrier, but only blocks one side of the unit and does not block any airflow (it has been there since the unit was installed).
    The unit was installed in May of 2011 and the pool is open from May thru September every year.
    Does the unit need service of any sort? It has not been serviced since installation. Thank you in advance for your support!

    1. Good morning John-

      The defrost cycle(FS code) activates when the ambient air is in the low to mid 40’s or 50’s depending on weather & site conditions. A defrost code in warm temperatures would most likely involve the defrost sensor or microprocessor and require service. Please contact us at 727-823-5642 to schedule service for your unit.

  23. Hi
    My pool heater has been working fine up until yesterday. The fan has always been working a and then yesterday the compressor has started and stopped as if a breaker was tripped ( it was not). This morning I decided to clean the unit w a garden hose to see if that helped anything and now ( a few.hours later) it has completely shut off help!

    1. Good morning Patty-

      Please contact AquaCal customer service at 727.823.5642 to talk to one of our technicians, they will be able to help you.

  24. My heater started up great at the beginning of the season (a month or so ago), heated the pool up nice for the kids. It has stopped running, and the code lights don't show anything (it looks like an ObA right now). help!

    1. Good morning-

      The message you are describing is “OtA” over temperature alarm and will require service. Please contact us at 727-823-5642 to schedule an appointment.

  25. I am having issues with the heat pump not being able to get a temp higher than 90 degrees. The heater will just stay running and not go above that temp. The red light indicating the compressor is on, and I can hear when it starts. The water coming out of the return into the pool seems not to be as hot as I remember it being last year. Had a HVAC tech stop by and check the Freon levels and top it off, and it is still not going above that temp. Any help?

    1. Hello Mike,

      If an HVAC technician simply topped off the freon level, this could indicate a refrigerant leak. If there is a leak, topping off a freon level would only be a temporary fix requiring the source of the leak to be located and brazed. Also, the heat pump is critically charged and if the unit didn’t have a leak, arbitrarily adding Freon could result in a overcharge. Both cases can cause performance loss. If you would like for us to have someone come and look at your unit just provide us with contact information and we will be happy to arrange this for you.

  26. i have a problem with my pool heat pump,it run for about 20 mins then stops and shows an error EE2 and in the handbook says low pressure. is this gas pressure or water,and how would i solve it. this is a dream heat pump. thanks tim.

    1. Hello Tim,
      Thank you for contacting us. The low pressure error message would typically show up as “LP” or “LP5”. This can be caused by low Freon pressure, a sensor issue, or icing on the outside of the unit. Low ambient air temperature can contribute to this error. Please call us at 727-823-5642 and we will be happy to assist you in more detail.

  27. My heat pump was running fine, now it turns on, then off then on then off and does this non stop. It was running fine, I am not sure what happened. The water flow pressure is 20 on the gauge.

    1. Good day Kent- Please try the following troubleshooting steps to correct the issue:

      1. Do you have a variable speed pump?
      If yes, go to next line. If no continue with trouble shooting after VSP questions.

      2. Does the lowest RPM setting take the flow rate below 30 GPM (or 20 GPM for T55/T75)?
      If Unknown, consult with local pool professional to determine flow rate.
      If Yes, adjust lowest RPM setting to get at least 30 GPM (or 20 GPM for T55/T75) flowing to the heat pump.
      If no, continue with troubleshooting
      1. Have you confirmed the isolation valves are in the correct position to allow water to flow through the heater?
      If Yes, proceed to question 2
      If No: confirm positioning

      2. Have you checked to make sure filter is clean?
      If Yes, set up service call
      If No: check filter is clean

      3. Is water level in pool at least half way up the skimmer?
      Y – Set up service call
      N – Confirm and call back

      Should these steps not fix your issue please feel free to follow this link“” target=”_blank”>(“ target=”_blank”>” target=”_blank”>( to speak to one of our technical professionals for further investigation.

    1. Good morning Mr. Redman,

      We are happy to hear this article was helpful to you! Please feel free to look through our other blogs and should you have any questions please do not hesitate to leave a message or contact us directly.

    1. Good afternoon Mr. Jones-

      We will be happy to help you with this, if you can provide us with an email address and/or phone number (and your location) we can put you in contact with someone in your area, please let us know.

      Thank you!

  28. Morning – my AquaCal heat pump is 2years old. Temperature here this morning is a cool 65 degrees with the heater set on 88 (as usual). Water is not heating and red light is not coming on. I have recycled several times, but still no hot water? Pump/fan has been running for about 2 hours now…

    1. Good afternoon Mike-

      The pool will not be heated if the red light is not “On” and that is because the compressor is not running, this could be caused by one of the electrical components or the compressor itself. We can have someone contact you regarding this issue, please provide us with a phone number or an email address and we will be happy to do so.

      Thank you!

  29. Hi There,
    I recently went away and my kreepy krauly sucked in the pool thermometer and blocked itself. The pump ran dry and my heat pump ran for a week without any water. Needless to say it now seems to be running all the time and doesn't have the heat input it used to. My electricity bill has rocketed also. The compressor is working and there seems to be heat going in to the heat exchanger but only a little heat coming into the pool and the air temp out of the pump is only marginally cooler than ambient. Can you advise where I should look or where the problem might be please?
    Many thanks,

    1. Good afternoon John-

      Two issues….the unit should not be able to run without water flow, so, the first problem to solve would be why it did so.
      Could be an adjustment or the water flow switch needing replaced.

      Then, it is most likely that the fan is running but the actual compressor is not based on the temperature conditions (air and water) noted.

      This would need to be addressed by a refrigeration/AC technician. If you would like help locating someone near you please follow this link:

      Please feel free to contact us again should you need further help.

  30. Good morning!

    If the fan is running but the air temp in and out is the same then the compressor is not coming on. This will require a technician trained in refrigeration equipment to diagnose. Likely a capacitor or relay issue but could be the compressor itself. To schedule a service call or find a local service technician please follow this link

    Thank you for contacting us!

  31. hi there 🙂
    my problem the air temps is the same in and out ,I went on vacation I turn off the heat pump for 5 days when I got back turn it on and since then not working (before everything was fine) now the fan running and all look good ,I cleaned all around the heat pump but same (delta t) what the problem ?

      1. Thank you very much for your input Lauri. Rick, if you are still having this issue please do not hesitate to contact us, we would be happy to help you!

  32. Where do I measure the temperature difference between air entering and exiting heat exchanger.
    Water temperature in pool doesnot get to 30 degrees Centigrade.

    1. Good morning-

      Air temperature entering should be read at three points around the circumference of the air coil, half way up vertically. Average those three measures for entering air temp. Discharge air should be measured right at the surface of the wire fan guard at the top of the unit, again, three points around the area of the guard. Average those three for discharge air temp. Difference is the delta T…

      We hope this helps answer your question, please do not hesitate to contact us if you have any further questions.

    2. Water and Air flow good. Outdoor temp approx. 80 degrees. Fan running fine. Water Temp readout is 82, heater set at 94 (pump running for 12+ hours), in-pool temp is showing 86. I am not sure why the pool is not heating-up like usual, and why the difference between Heat Pump temp reading and actual pool water reading…

      Usually in this hot weather, its hard to keep the water from being overheated, now I can’t get it past 86 running the heater all night.

      Any ideas? Do you have local service people in Metro-Detroit, Michigan? Thanks!

      1. Hi Jason,
        If the heat pump is running properly, you should feel cool air blowing from the fan while the compressor is on (i.e heating light is on). The air should be 10 – 12 degf cooler than the ambient air. You should also notice condensation under the unit. Please call us at 727-823-5642 and we can assist with troubleshooting and locating service centers in your area.

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