Atwood gas water heater leaks when turned on

ezgoin wrote:
Will the heater have to be removed for examination?

Yes. Not difficult but does take a bit of time. Assuming the water line fittings themselves aren't the source of the problem the aluminum tank itself is either split or there could be a hairline crack in the welds where the water lines connect to the tank. I helped a friend remove his Atwood water tank with this exact issue, fortunately in his case the hairline crack was successfully welded. If in your case you determine that welding isn't practical the good news is that Atwood does sell replacement tanks, with Suburban you'd have to replace the entire water heater. BTW, in the process of removing the tank you'll destroy the gaskets and rings that hold the tank in place to the mounting plate ... new replacement tanks include this ring & gasket kit but if you manage to repair your original tank this ring & gasket kit can be ordered from any RV dealer.

Maybe the PT valve is bad and the overflow pipe is leaking. Just a guess.