It sounds like a transducer problem. on a different unit I had it read the depth and then all of a sudden it said I was in 36 feet of water and I was in like 3 feet. I could see the bottom. The water temp stayed the same. I tried resetting the unit. I was going crazy trying to figure out the problem it was like the unit was in demo mode but could find a setting like that. Then upon further investigation I realized the transducer plug wasn't pushed all the way in on the back of the unit. Once I pushed it in it was working fine . Maybe you have a bad connection or a broken wire like bowhunter already mentioned .