Hayward Heater Flashes "LO" when solar turns on

When my solar heater turns on, my heater stops working, the service light comes on and the LED displays "LO" . I see from doing some reading that this means the flow sensor has low flow. The filters are not dirty as this is a brand new pool. Is this normal? Can the solar and the heater not be on at the same time?


LifeTime Supporter
Platinum Supporter
TFP Expert
May 7, 2007
Silver Spring, MD
It is difficult to say. Some of this is adjustable and some isn't, with many of the details being unique to each pool and thus difficult for us to predict. Most pools do not have this issue, but it is possible that there is nothing you can do about it without replacing some equipment, again depending on details we can't figure out easily and must be discovered by experimenting.

When the solar system turns on the flow rate will go down, how much the flow rate goes down depends on a number of factors, some of which you can adjust and some of which are built into the design of your plumbing system. Solar systems usually have an adjustable diverter valve that controls how much water goes to the panels and how much goes directly to the pool. Adjusting the system so that more water goes directly to the pool will increase the flow rate. However, there is a limit to how much of that you can do without losing most or all of your solar heating. The only way to find out is to experiment with your system.

Other factors can affect flow rate, for example clogged skimmer baskets or a dirty filter. These might cause the symptom to only happen occasionally.
Thanks for the reply...my solar guy keeps saying I need a better pump. He has nothing to gain from it since my pool contractor would be swapping it. I currently have a Hayward 1hp Superpump and my solar guy says the Hayward Tristar 3/4 hp pump is more energy efficient and has a greater flow rate. I had no idea a pump with a lower hp rating could create more flow! He says (just spoke with him before I posted) this will create enough flow to get rid of this "LO" message and allow solar and heater to work together if need be.

Do you think he is right? Is it worth it to upgrade to this pump? I think it'll be about $250.