A couple of quick checks I use include looking for a steady stream of very small bubbles coming out of a return, if the bubbles are there the cell is generating, also you can capture a water sample right in the return stream and test the chlorine level, it should be higher than the pools overall level. In both cases make sure your SWG shows the cell is on before checking, if not on I bump my output to 100% while checking the SWG then return it back to the previous level once done.