I just got these two error codes a few days ago (120 & 121). I tested my cell and flow sensor and i got some weird data. My cell voltage read 14v. It reads the same from where the cord connects to the board. But when i test port 4&5 it reads 0. Ive cleaned the flow censor and the cell also. My question is, wouldn't i get a different code if I had a bad board? i have the old 2 port cell. Im contemplating if I should just by a whole new system if i have to replace the cell. I had the unit for 4 years. What do you think?