I have been on a quest for the last few months to get my SWGC (Pentair IC40) working properly. I went through everything and ultimately had my builder come out and replace the cell (it was still under warranty). I wanted to memorialize for anyone else searching what I found.
The cell itself did need replacing. It was manufactured in 2008, but not installed until we built in 2010. No matter what I did, the "Cell" light indicating chlorine generation would not come on. The cell was clean and all other aspects worked fine with our EasyTouch 8 system. After the cell was replaced, it worked for a couple of hours then quit.
I noticed after the cell was replaced that the water temperature sensor was reading randomly between -22 and 40 degrees F. It's important to note that the "cold/freeze protection" light on the cell was NOT coming on. The air temperature sensor was working correctly. After re-reading all the manuals and noting that the cell will not generate below 52 degrees, I suspected that the very low temp readings were preventing the cell from being activated (even though the "cold" light was not on) I swapped the air temp leads and the water temp leads and voila! It worked. I obtained a replacement sensor for $30 and it corrected the issue permanently.
One other note: the cell will not operate unless the "pool" function on the EasyTouch is on. Maybe it was just me, but I didn't read anything in the manual that made this clear. But it is the case.
So, after replacing the cell, getting a working water temperature sensor and making sure the Pool function was on, all is well.
Hope this helps someone in the future.