Solar Pool Heating Water Temperature Sensor

How a Solar Pool Heating Automation System (Controller) Works

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A solar pool heating controller automatically turns a valve using a motorized actuator. It is the best way to maximize solar pool heating performance and provide convenience. Most pool automation systems have solar pool heating control built in, so you don’t have to buy a separate controller. Solar controllers can be simple thermostat-style controllers or can have advanced features to automate other pool equipment. Learn more below about how a solar pool heating controller works.

Here is a list of some popular solar controllers and pool automation systems that include solar control:

  • Pentair SunTouch
  • Pentair SolarTouch
  • Pentair EasyTouch
  • Pentair IntelliTouch
  • Hayward GL-235
  • Hayward OnCommand
  • Hayward AquaLogic
  • Hayward ProLogic
  • Hayward E-Command 4
  • Hayward AquaPlus
  • Hayward OmniLogic
  • Jandy Aqualink
  • HelioTrope HelioMatic

You can also learn more about how a solar pool heating system works here.


  1. I want to get a solar controller for my solar pool heater, but can I add it after it is already installed? Do you need to put a new valve? I have one speed pump now and might decide to get a variable speed in the future. What can I do?

    1. Author

      Hi Salvatore,

      Yes, you can add a solar controller after your solar pool heating system is already installed. Your installer will have included a bypass valve, also known as a Jandy valve (for the popular brand). A motorized actuator can be screwed to the valve after four of the eight existing screws and handle are removed. The actuator will connect to your new controller and turn the valve based on the need for solar heating.

      As for the pump, I recommend installing automation products compatible with the pump brand you are considering. For example, a Pentair Intelliflo VS pump will work best with a Pentair SolarTouch, SunTouch, Intellitouch, EasyTouch, etc. That’s not to say that other automation products can’t control the Intelliflo, but there may be an interface module required. Some brands of automation natively control other brands of pump. For example, the Jandy Aqualink controller (with newer firmware versions) will control the Pentair Intelliflo with a digital interface cable and no intermediate module required.

      I hope that helps!

  2. I am buying a new solar system and 2 different dealers are offering me the same panels but different solar controllers. One is offering a Hayward Aqua Solar automatic thermostat complete with set up. GL235 control and the other is offering a Solar Touch by Pentair.

    Which one is better or are the equivalent. Thanks

    1. Author

      For a few bucks more, go with the digital SolarTouch. It can natively control a Pentair variable speed pump later if you decide to upgrade. The GL235 is a basic control with an analog temperature dial.

      1. Thanks

        Both do the same but one is digital and the other is analog? That is difference?

        If I want to move to a variable speed pump next year can they both handle that?

        1. Author

          The GL235 does not have Digital pump control, so it can only command 1 speed of an analog pump like the Hayward Ecostar. You will not be able to select a third speed with the Hayward pump for things like cleaning the pool. That is why I prefer the Pentair controller and pump.

          Otherwise, they do essentially the same thing. we offer both, but rarely sell a GL235. Both are quality products.

        2. Author

          By the way, it is pretty rare to have two dealers for the same brand of solar panels in a single territory. Can I ask what market you are located in?

          1. You asked what market it is Tampa/ Land o lakes area

  3. Author

    Mitchell: Thanks – I recommend you call Coast to Coast Solar if they are not already one of the dealers. They will probably tell you to go with the SolarTouch. It really depends on your future plans. When you go to replace your single speed pump you are going to be forced by building code to upgrade to a multi-speed or variable speed pump, so making your control compatible with your future plans is key.

  4. Is it possible to add second sensor for solar control? The sun gets passed the sensor but it’s still on the panels but it turns off, I’m missing a lot of precious Soler Heat.

    1. Author

      Not possible. You can relocate the sensor or adjust the start/stop differentials.

  5. Hi, really nice your page, information and connection diagrams. Thanks.

    I have a question, I saw that some controllers (pre made or DIY ones, which is something I am building at home) have the roof sensor in the pipe, just below the panel finish, when the hot water is returning to the pool. In your diagram it shows that you have a simple roof to get the sun temperature right? With a insert pipe pool temp only.
    Wouldn’t be useful to have the hot solar water temperature also? Or use that to make the calcs and decisions? Thank you

    1. Author

      This is an excellent observation and an improvement that I would like to see differential solar controller manufacturers implement. It would be helpful to know that the roof temperature is warmer than the pool water, but also that the warmed water returning to the pool is actually being heated, or heated sufficiently. Additional logic could be implemented to recognize when the conditions are marginal and minimal heating is being accomplished. This would allow variable speed pumps to drop down to lower speeds and turn off the solar panels when conditions are marginal. You could also program in some logic for auxiliary heating to kick in if solar is heating too slowly. The most complicated part is building in delays or somehow averaging the readings from the heated water. Instantaneous readings would cause the controller to turn solar off and on too frequently. It’s not a simple problem, but I really like the thought of, at a minimum, being able to see the temperature of the water being returned to the pool.

      However, I don’t think the 10kohm sensors commonly used are precise enough for this purpose. The problem is that solar-heated water should only be a small bit warmer than the water going into the panels. You want a high flow rate and a small temperature rise for each cycle of water through the system. This further complicates things because flow rate would need to be taken into account. You could actually slow the pump down (to an extent) to achieve an optimal temperature rise.

      In the end, I think it would be hard to implement, but it’s definitely something to consider. For now, the differential controllers on the market fall into the “good enough” category when properly installed and programmed.

  6. A couple of years ago you recommended the digital SolarTouch to control a solar system. Is this still the best option? I currently have a single speed 3/4 HP Jandy pump but will be upgrading to a variable speed unit at some point. The pool is small (7500 gallons) so we have large temperature swings when relying on manually diverting water to the panels. I think adding an automated system is the way to go. Thanks!

    1. Author

      Jim: Yes, the answer is still the same. You can use the SolarTouch with your single speed pump. When you upgrade you will probably want a Pentair Superflo VS with the optional comm cable and a qualified installer to install it properly. You could upgrade to the Intelliflo VSF for a lot of added functionality and less noise, perhaps better life and better warranty for a few hundred dollars more (and it comes with the proper cable). It sounds like either would work well in your scenario.

  7. Hi,
    Great site with simple but precise explanations. Well done!
    I have solar heating which currently I control manually.
    I’m thinking to install a controller which should simply measure the pool and the solar panels’ returning water and decide whether to direct the 3-way valve to the panels or not.
    No need to connect it to either the filter pump (fixed speed anyway) or to the heating pump (works based on its own thermostat).
    From what I read here, both Hayward’s GL235 and Pentair’s Solar Touch will do the job fine (understand the differences you pointed out which in my case don’t really matter much. Probably will go with the longer warranty…).
    What I’m not quite sure is what will happen when my pump switches off (controlled by a mechanical timer)?
    In which position will the 3-way valve be? Does it matter?
    Thank in advance,

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