Solar Pool Heating Troubleshooting Guide

Why Isn't My Solar Pool Heater Heating the Pool?

Article was written by Gregory Grochola (physicist) - last updated 17/10/2026

Is your solar pool heating system working technically, yet it's not quite boosting the pool's water temperature to what you expect? In this guide we go through a comprehensive list of troubleshooting points to help you track down why your solar pool heating system might not be running as efficiently as it could be.

Solar mats or panels should be cool or only slightly warm to the touch with the water running and sun on them. If sections of your collector are hot to the touch, that means there is insufficient water flowing through that section. To perform a hot spot check, jump up on your roof at 12 noon with the sun blazing down on your collectors and the system running, and run your hand over all parts of the collector system.

Do you feel any hot regions? If yes, your collectors are bleeding heat to the sky and are not working as efficiently as possible. All materials emit black body radiation, and the hotter the material, the higher the heat loss.

If you do a hot spot check and the collectors are cool with the sun blazing on them, then you can be confident that they are pulling the heat off the roof and into your pool. Our installation manuals describe the same check, see Checking for Balanced Water Flow in the OKU panel manual or the PoolMasterPro strip manual.

Sometimes the collector array is not quite set up correctly, perhaps there is no third balance pipe installed on a strip heating system, or the inlet and outlet points on an OKU panel array are set up wrong. Check here for how not to set up a strip system, and here for how not to set up panels. Common issues include air locks, inappropriately sloped collector sections (depending on the collector type) and short circuiting situations where the bulk of the water only flows through one part of the collector array.

Sometimes strip systems draw from a suction port but are installed without a pre-filter (in-line strainer) and they get twigs and gunk stuck inside. Check the water flow through the tubes by feel: are they hot, or is there water flowing inside? Some studies also show that there must be a set minimum flow rate through a tube to push air out of a horizontally running tube system. This is more of an issue for strips with bore diameters larger than 8mm, but if your strips sag across a Flatdek valley and you combine this with a low flow rate for the system in general, this can slow the flow in any one particular tube length and create air locks, where some tubes will not have any flow in them at all. Diagnose by feel: are the tubes hot in the sun with the system on? If so, try increasing the flow rate to clear any air locks you suspect.

Strip collectors sometimes run with a slower flow, as they have to push water through tiny tubes, and this can create a larger temperature differential. If you have one of these systems and you can't increase the flow, it's handy to run your filter pump right up to the late afternoon and direct the return flow downward to help mix the warm layer of water that develops during the day. This stops the excessive losses overnight to some degree and offsets the inefficiency in the system. See also our post on removing your pool's eyelet socket.

Sometimes people expect manual operation to produce the same heat as an automatic system, but that's not the case; an automatic system will be able to turn the system ON and OFF depending on whether or not there is heat to be gained. This prevents cooling during chilly or windy spring and autumn days. See our pool solar controller guide for the options.

Secondly, are you running the solar opportunistically, i.e., just before the weekend trying to heat up a pool? This will also produce dramatically lower pool temperatures, because people don't realize that the ground around the pool contains a great deal of thermal mass, and it takes a week or so to heat up.

A solar system that is allowed to run all week will make the ground around the pool come to a new equilibrium temperature. Once the ground around the pool is warm, this stops the pool from losing heat through the walls excessively. Try to warm it up on Friday hoping to have it warm on Sunday and you'll find the cold ground will suck the heat right out of the pool.

Some people or installers get it wrong. The updated Australian Standard (AS 3634) still gives a near flat 100% sizing recommendation without taking into consideration the specific heat loading characteristics of the pool in question. We questioned this at the last round of pool heating standard changes, but our changes were not adopted.

Our sizing calculator and water temperature simulator do a great job of boosting collector sizing when there are multiple adverse heat loading conditions, and sizing it down whenever they can to prevent oversizing. Try it and see what sizing and what pool temperature you get, and compare it to the collector size you have. You may need to add more collectors, or you may find there is a heat loading factor that's severely affecting your pool, like wind/sheltering (which is a large one) or shading.

Another large factor is wind exposure and local area factors. Wind will strip heat off the surface of a pool very quickly through evaporation. This might explain your pool as well. Pools exposed to wind get a large temperature boost from a solar blanket, which cuts the evaporation rate. The simulator lets you set how exposed or sheltered your pool is, so have a play with it.

We've also seen some very dusty collectors. This will be dramatically affecting the collectors' efficiency, not only because the dust shades the collectors, but it also forms an insulating layer that takes the heat from the sun, heats up and doesn't pass it on to the collectors. Perhaps try washing the dust off, if it's safe to get up on the roof.