I saw your post about the problem with your Readdy heater. It sounds exactly like the problem I just fixed with both of the heaters I"ve got and I didn"t sere this problem addressed. I agree with some that the photo cell can be a problem, along with dry rotted lines causing it ti lose suction, but before you go buying parts try one more thing. If you look where the suction line goes through into the tank there is a rubber grommet, take a screwdriver and pry the grommet out along with the pickup tube going though it. Inside that pickup tube is a screen and if it"s like mine it"s a conical in shape with the pointed end up. With mine all I had to do was tap the tube on the table and the screen came out. If you can get it out that"s the best way to clean it because the crap will get built up in the top of the cone and not want to come out, but if not then backflush it with brakeclean, blow back through it with compressed air, etc. Whatever you do just make sure it"s clear. In my case the screens were clogged nearly to the point of being completely closed up but my heaters would still run for a few minutes, sometimes up to an hour, before quitting. I had tried everything else, cleaning photo cell, etc and nothing worked until I discoverd the screens and cleaned them out. Now the heaters run like they are supposed to. If nothing else worked, I hope this helps solve your problem.