Hayward AquaSolar Control, GL-235

The Hayward GL-235 AquaSolar is a dual differential control for solar heating of pools, spas and hot tubs. It decides when the solar panels are worth using and manages the system from there.

How differential control works

A solar panel is only useful while it is hotter than the water. The control reads both temperatures and calls for solar when the difference is in your favor, then stops when it is not. Without that logic a solar loop happily pumps water through cold panels at dusk and cools the pool it was meant to heat.

The rest of the feature set

A selectable high limit caps how warm the water gets, so the system stops adding heat at your chosen temperature instead of running all afternoon. Freeze protection is programmable, which matters anywhere a night can drop below freezing with water sitting in the panels. Automatic nocturnal cooling runs the loop after dark to dump heat, which is the fix for pools that overheat in hot climates.

Where it fits

The same control is used on pools, spas and hot tubs, so a single unit handles most residential solar installations.