JamesW and others will know much more on the electronics and possibilities, but the below is from a ProLogic diagnostics manual manual. While waiting on other ideas it may be worth trying the reset just in case. I CAN confirm that when I last checked my cell to see if I needed to clean it I verified it was off, then unplugged it, but the controller was still on. I got low temp, low salt, AND high salt errors and the reset cleared them all.
2. If the controller is still powered, when unplugging the cell and then the cell is subsequently plugged
back in, it may display a ‘Low Temp’ fault message and the ‘Check System’ light may still illuminate.
Turn the filter pump on. You must reset the system by entering the ‘Diagnostic Menu’ and then hitting
the right arrow key once and then pushing the plus key once. This should reset the light and message.[/QUOTE
When you do this it counts Down from 15 and tries to come on them immediately turns off and says. Low temp chlorinator off. I cleaned it replaced with new swg and still Same error. I think with replacing the transformer and rectifiers. The only thing left is the relays or the pcb board.