I have a similar issue as described in old thread. The conclusion in that thread was that the SWG was bad and Pentair replaced it.
Some days my SWG reads 3300 - 3400 other days it reads zero. This has been going on for a few weeks. One time I got the zero reading the day after I added 40 pounds of salt. Last weekend I took a water sample to a nearby pool store. He uses a Taylor test kit for everything but salt. For salt he has some fancy $500 machine. Anyway, he got 3250 for salt and I was getting 3300 from the IC 40 that day.
So I called my PB (I'm about 30 days from my 3 year warranty running out) and told them that my SWG is acting up and warranty needs to come out and replace it. Their theory is that the SWG and the DE filter need to be cleaned. I've never cleaned my filter although I backwash every month. I haven't cleaned the SWG although I inspect it periodically and have never seen any signs of build up. They are coming out next Tuesday to clean the SWG and the filter. I generally trust my PB but I'm suspicious of this diagnosis, primarily because I've read so many threads that describe what I'm experiencing and the solution was a new SWG.
I've got time to watch the SWG for a few weeks after they do this cleaning for me. So if it doesn't fix the issue I should be able to get the SWG replaced under the warranty. Just curious on opinions about the diagnosis.