Pool Plumbing with Solar Pool Heater Explained

Pool Valves With Solar Pool Heating Explained

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Pool Plumbing with Solar Pool Heater Explained

A typical pool plumbing system with solar pool heating.

How Swimming Pool Valves Work

With so many people moving to Florida and owning their first pool, it’s not surprising that a majority of pool owners are baffled by their swimming pool plumbing system. When we endeavor to add solar pool heating, the plumbing at the pool equipment pad becomes a bit more complex, but it’s not too hard to understand your plumbing and valves once you understand which way the water flows through each pipe. In this article we attempt to explain the basics of how pool valves work with solar pool heating, and what all of the plumbing does.

When you have a solar pool heater, valves can be broken down into three groups.

  • Pool Suction Valves – these valves control pipes that suck water out of your pool.
  • Solar Valve Manifold – these valves divert water to solar panels, or stop water from entering solar panels.
  • Pool Return Valves – these valves control through which jets and features water is returned to the pool.

Diagrams of Pool Valves with Solar Pool Heating


  1. Suction Valves

The suction valves control from where water comes into your pump. You can tell which valves are the suction valves because they enter the pump horizontally. The vertical pipe out of the pump is for water coming out of the pump — the discharge side of the pump. Typical suction valves include main drain(s), skimmer(s), suction cleaner(s) (vacuums), and spa suction for pool/spa combinations. These are all of the places that water can be drawn out of your pool.

  1. Pool Pump

Your pool pump circulates water through the filter, solar panels, auxiliary heater, and chlorination system (not pictured). The pump can be a single speed, two-speed, or variable speed pump model, and it is sized to provide adequate water circulation and filtration for your pool and pool features.

  1. Pool Filter

The pool filter takes physical contaminants out of your pool. This may be a cartridge filter (most common), sand filter, or diatomaceous earth filter.

  1. Solar Valve Manifold
    Solar Pool Heating Valves Close Up

    1. Filter Check Valve
    2. Solar Diverter Valve (aka 3-way valve, bypass valve, solar valve)
    3. Solar Isolation Valve
    4. Solar Return Check Valve

Every well designed solar pool heating system should include four valves for proper directional control, diversion, and isolation.

The first check valve, which allows water to flow only one direction) prevents water from back washing the filter into your pool. When the pump turns off, water drops from the roof mounted solar collectors, and if this check valve was not present, debris in your filter would go back to your pool through the suction plumbing.

The solar diverter valve controls whether water goes up to the solar panels or goes back to the pool without entering the solar panels. There is (should be) a tiny hole in this valve that allows water to drain back to the pool when the pump shuts off. The water drains through the hole and back to the pool through the return plumbing This hold is small enough that only a small amount of water can pass through it when the valve is in the closed position.

The solar isolation valve prevents any water from entering the solar panels. This is important for service purposes and to positively isolate your emptied solar panels when not in use for extended periods of time. Remember that the solar diverter valve has a small hole in it, so without this valve there would be no way to prevent all water from entering the solar panels.

The return check valve allows water to only come down from the roof in this plumbing line. This stops water from going up the return line when the solar diverter valve is in the off position and your solar pool heater is not operating.

Note that this valve manifold may be flipped left to right with the solar diverter valve on the right side depending on the location of the solar panels relative to the pool equipment.

  1. Auxiliary Heater (optional)

Your pool may already have a gas heater or electric heat pump pool heater before you install your solar energy system, or an auxiliary heater may be installed to supplement solar heating depending on your particular circumstance. The auxiliary heater is completely optional with solar pool heaters, but most people with a spa want a traditional heater to quickly heat a spa on demand.

  1. Pool Return Valves

These valves control where water is returned the the pool. The valves can turn on and off the side jets, fountains, waterfalls, bubblers, therapy jets, spa spillovers, and other pool water features.

Pool Plumbing Valve Operation

Pool circulation during normal operation.

Your pool may have a different plumbing and valve configuration, and pools with lots of features can be quite complicated. Pools with attached spas will also have additional 3-way valves to control the spa operation (see below). Some pools only have a single suction and/or single return line, and some suction and return lines may not have valves on them at all. Also, some suction and return valve manifolds may use 3-way valves to reduce the number of valves required and provide extra functionality in selecting a water source or feature return. Valves can also be used to control the flow through features, like the height of a fountain.

Solar Pool Heater Plumbing with Spa

Solar Pool Heater Plumbing with Spa

In the above diagram, there is a 3-way valve on the suction side and the return side that controls spa operation. When the spa is being used, the typical desired configuration is to isolate the spa so the pump only draws water from the spa and returns all of that water to the spa only without a spillover. That way you can heat the spa independently from the pool and maximize the flow rate through the spa jets. In the valve configuration above the pool is in normal operating mode, drawing water from the pool only and returning water to both the spa and another pool jet or feature. This way the pool owner can circulate the spa and pool simultaneously and have a nice spa spillover effect.

Pool plumbing systems are as diverse as the pool builders who build them. You will see all kinds of different valve and plumbing configuration based on the budget, installer skill, philosophy, components, and overall system design. Even solar pool heating manifolds differ. For example, some installers prefer the diverter valve on the return line.

We have explained pool valves with solar pool heating systems. If you have questions specific to your pool equipment, post your comments below and we will do our best to help you!


  1. if I want to truly isolate water flow to/from my solar panels should I have 1 valve for water to panels and 1 valve leaving panels?

    1. Author

      You can use an isolation valve on the feed line and a check valve on the return.

      Installing an isolation valve on the turn can cause your system to be “dead headed” if the wrong valve is closed, causing excessive pressure and pump or panel failure.

  2. which way should water flow in a pool when there is a solar heating system?

    East to West?
    West to East?
    From floor to Up?
    From Up to floor?

    (Its a question on my exam that i did not understand)

    1. Author

      Hi Matt – I honestly have no idea what that means. Was that the actual question on a test?

  3. Hi, in my solar pool heater setup, there’s a thin tube (about half inch diameter) about half way up the wall that connects the return pipe (the ones bringing the hot water from the roof) with the supply pipe (the one taking the water up to the solar panels). Any idea what function this connector serves? the tube is connected at each end (of the PVC pipes through a small plastic connector (a tube with a cylindrical tab in the middle). One of these connectors is broken. Any idea where I can get a replacement one?

    1. Author

      You have an old school drain down bypass. This allows the system to drain when the pump turns off. We now install valve manifolds with either check valves or holes in the bypass valve to fulfill the same function. I have no idea what connector you have, but any plumbing replacement that fulfills the same function will work, or abandon it and drill a 3/16″ hole in the gate or ball of your solar bypass valve.

  4. I just had a Hayward salt chlorinator installed and now there is water going to my solar panels when the valve is off. Prior to install it never happened and the pump was running at a higher speed. I know this because I have a small leak in panels so I’ve had it off waiting for repair. Wake up the first morning of install and find water running off my roof. Why would installing a new chlorinator force water past closed valve? Very perplexing! Thanks for your help.

    1. Author

      Hi Mr. B,

      That’s hard to say without looking at it, but it sounds like either your installer removed a check valve on the return line from the solar or left a valve in the wrong position. I will email you and you can send me a picture of your equipment.

  5. How do I stop water from flowing to the solar heater? One of the pipes on the roof has developed a leak.

    1. Author

      Hi Debbie,

      Based on your name and email address I don’t believe you are one of our clients. Our competitors routinely do not install proper isolation valves, so it may not be possible to stop water from reaching the roof, especially up the return line from the solar panels. We install a solar bypass valve and an isolation valve on the feed line. The return line has a check valve that prevents water from reaching the panels in reverse. Unfortunately, I have to advise you to turn your pump off and contact a solar professional or pool service in your area. If you are in Southwest Florida, call us at (239) 491-8010 and we can help.

  6. Hi – very helpful site. You did not install my system (I’m in Florida, but north of your region). I have an issue with water staying up in the panels when the solar valve automatically shuts off (temp is reached), but the pump is still running. This is causing the water to over heat and making my rubber bibs / fittings to burst causing leaks. When I go on the roof this water is really hot. We recently had a solar company change the three way valve by installing one with a check valve (instead of just a hole).

    Now when the pump turns off I get complete drain from the solar panels. This new valve also prevents water from still going up when the solar turns off, but the pump still running (compared to my old one that had a small hole and still allowed water to go up when the solar is off). However, I still have the same issue as before when the the solar turns on early in the day and then turns off when the temp is reached within an hour (88 degrees). In most cases my pump is still running for another 5 to 6 hours preventing water from draining back and causing this boiling effect.

    How do we get water to drain back down even when the pump is still running? We’ve had numerous pvc fittings and bibs give out since installation. We have a Hayward singe speed pump and filter that runs at about 32 PSI. My automation systems is a Jandy, but have an automated Hayward actuator for the three way solar valve. We have two sets of panel (5 each and are 12 feet long each, for a total of 10 panels). My pool is about 19,000 gallons and both sets of panels are on the first floor.

    This is getting very frustrating and would appreciate any help, advice, and recommendations on what to do next. The solar company is still investigating as well.


    1. Author

      Hi Joey,

      First, I’m not sure exactly what you mean by “bibs.” But I’ll answer your question anyway. A solar pool heating system is typically designed to handle the temperature of stagnated water that is in the system under the conditions you mentioned. I’m guessing you have black PVC plumbing on the roof. Black PVC fittings and pipe are not a great idea because they are not as resistant to heat as white schedule 40 PVC. Black fittings can split where they are molded together as the PVC pipe swells.

      It sounds like you are trying to drain the panels when the pump is running. That isn’t going to happen. It’s impossible without having a completely separate plumbing drain line going back to your pool, which pools are not built with. The solution is actually the opposite of what you are attempting to do. What you want is a larger hole. You should allow a small amount of water to flow through the system when the temperature is reached and solar is off. This small amount of water will not heat your pool much but will keep the water in the panels circulating.

      But ultimately, the system should be designed to handle the stagnation temperature of water trapped in the panels. It will not “boil” as the stagnation temperature is well below 212ºF.

      And if I’m right and you have black PVC, consider replacing it. We only install it when HOAs require it and customers absolutely demand it. It’s a terrible idea. I keep telling people, but nobody wants to listen.

  7. Bibs as in the black rubber fittings that connect the solar panels to each other.

    Yes, I have black pvc, per HOA and because the panels are black. The new modifications were recommended by the manufacture of the panels. The frustrating part is my neighbor across the street has the same system done by the same company and they have no issues. Every three weeks or less I have a new leak. Only difference is my pool is bigger, I have more panels, and I have the cleaning pop-up heads that also act as my returns for the pool.

    Maybe boiling is exaggerating a bit on my part, but the water is very hot when I go to the leak on the roof. I can’t keep my finger over the hole for more than a second or two.

    The manufacture recommended the three way valve with built in check valve, instead of the hole, because I have very long run of pipes and panels and they are all on the first floor (and we need assistance to drain back down to avoid the water stagnation). It’s working fine when it shuts off, but not when the water reaches the temp and the solar turns off, but the pump still running.

    I’ll bring up going back to the old method of the three way valve, but maybe with a bigger hole. We’ll see what else we need to do.

    Thanks again

  8. Joey, I have bad news for you. Pop up cleaners are a nightmare for solar pool heaters. The extremely high back pressure means that flow through the panels is very low, increasing temperature. This is a bad combination for plumbing, especially black plumbing. High temperature and high pressure is bad.

    Second potential issue: if you don’t have a check valve on the return line from the solar, you are going to seriously stress the plumbing and panels. Many (most) dealers don’t install a check valve, which I consider a requirement.

    Your best option is to bypass your pool cleaner popups (if possible). Abandon them.

    Pop up cleaners are pretty old school. They don’t work well and they are energy hogs (more pressure means more horsepower or more pump run time to achieve turnover). It sounds like your pool is older. You probably also have 1.5 inch plumbjng. Everything is working against you. High back pressure is a challenging problem.

    It’s unfortunate that you are not in my service territory, but there might not be much I could do to help. It’s truly a tough issue to resolve. You need to increase the flow and reduce the pressure in your solar panels and avoid high pressure stagnation.

  9. Yes, I do have a check valve on my return line. I also have one after the filter and now there’s a check valve built in on the three way solar valve. I also forgot to mention that I have two Vacuum Relief (VR) Valves. One in between both set of panels and another one at the end of the return line (closest to the return check valve). I also have a shut off valve (ball valve) above the three way where I can isolate water from going up to the solars/roof.

    The return from the solar actually goes into my heat pump (which I use for my spa during the off season).

    The problem that I see is that my pop up heads are my only returns in the pool (I don’t have dedicated standalone returns in my pool). I also have pop ups in my spa as one of the zones and the only other returns I have are two in my spa (which creates the spillover). So if I turn my pop up heads off (essentially turning the valve off), my only return would be in the spa via its two returns. So spreading the water flow would be poor (both in chemicals and heat spread). I guess it’s an option, but one that defeats the purpose I suppose.

    The previous owners built the pool around 2008. Not sure if 12 years is considered “old” in terms of technology, but I agree that the pop ups don’t really do its job. I didn’t build it, so I’m stuck with them.

    Any other recommendations based on the additional information I provided? Thanks.

  10. It just keeps getting worse. The heat pump inline with the solar return and no way to bypass it just introduces even more back pressure. Depending on the heat pump, it may have significant flow resistance.

    A lot of pool buyers and pool builders are now regretting pop up cleaners.

    It’s just a bad situation that the solar dealer should have recognized and addressed up front. You could use the Florida solar rights statute to convince your HOA that their restriction impedes the ability for you to have solar and increases the cost substantially. Replace everything with white PVC, increase all plumbing aboveground to 2 inches, and use panels with low back pressure (like the iSwim we offer). Bypass the heat pump. But you still might have issues with ballooning rubber couplings. If properly installed they should not leak.

    It’s a tough situation. Frankly, I would recommend a different approach – an efficient heat pump and enough solar electric panels to offset the utility electricity cost. Your system is not well suited to solar pool heating panels.

    I doubt you will be able to economically and permanently fix your frustrations.

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