DSI-FLT Light

I know this is a fault indicator associated with gas firing of the water heater. Now that’s out of the way, let me explain what’s happening. Regardless of whether I turn on the “electric” or “gas” switch, the heater will heat the water without failure and as soon as it’s hot (seems hotter than it should be) the light comes on. At this point, it doesn’t matter if I use the water to a point where it should be heating again, it will not heat until I turn it off, let it stay off until the water cools and then turn it back on. I’ve tried every variation!! So, I’m forced to turn it on 1/2 hour before needed and then turn switch off after it heats. One point is that the tstat was replaced last year, but this has just shown up. Too me, it screams that the tstat is not functioning properly and shutting off, when it reach proper temp and this is providing secondary safety. Before I replace the tstat, wanted to here from the wide world of RVr’s. Appreciate anything that can be offered.