Well, the dealer suggested we put in new heat sensors switch(?). But I read some where on here that thus furnace needs lots lp pressure and a pretty specific routine to installing a new tank and opening the valves after you do. So I changed out the tank and followed the op directions. First, turn the selector valve to the opposite tank. Connect the new tank. Open the new tank slowly. Turn the selector valve to the new tank, slowly. I guess you can open it to fast and the pressure "slams" into the regulator and selector valve.
Another question I have now is the tank that I replaced was only , roughly, 2/3s used. It still had quite a bit left in the tank... Hmmmm.
Thanks for listening.