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

    4a. Filter Check Valve
    4b. Solar Diverter Valve (aka 3-way valve, bypass valve, solar valve)
    4c. Solar Isolation Valve
    4d. 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 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

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!