The pressure valve on my water heater started acting up. I ordered a new one, but am having difficulty getting the old one off. I sprayed P-Blaster on it and still won't budge with my 6" wrench. I intend to bring a larger wrench, but am concerned about breaking it out of the tank. Anyone have an idea just how sturdy that tank is?

Of course, if I break it off, I can replace the whole water heater, but it still works just fine, has very little rust and replacement is a much bigger job if not necessary.