If the t&p valve is not leaking when you are looking at it, it's doing its job and probably not the problem. Put in an expansion tank and then check the t&p valve again.

I believed you when you said, " I replaced (the original tank), wired it as directed." Now, this new tidbit has me concerned about the whole electrical scheme. As I started to read your message, I expected that you were trying to say that there was a circuit taken off of one leg of the line. But you describe it as a line coming into the heater and powering one of the elements. That suggests that the other element is also powered by a simplex, 110-V circuit. If so, this needs rewiring as you have a seriously miswired condition. I suspect this because you said: "I tested the connections numerous times and always came up with 120, never 240" To get 240 V, you need to have two legs of the service wired into the heater. And this would put each (say, the Âblack and the ÂredÂ) on each heater, the upper and the lower. Since each of them has a second terminal, those are wired to the neutral (white) wire. If that is the case, that you have a 3- or 4-wire cable properly connected to the heater, then it means that the one element was not able to be shut down by the thermostat. Moreover, it also appears that the chance wiring has allowed the one element to be powered by 240V via the cord connection. Certainly, removing this cord is the right and the first thing to do. It appears that, for the first six hours, the new heater was being warmed by only one element. When the thermostat attempted to shut down both elements, the miswiring stopped one and started the other at doubled voltage. (Boom!) While a water heater is power with 240V, the elements operate independently at 120V, each. They should never see 240V, unlike the heating element in a clothes dryer. Now, if the unit is properly wired, you can test voltage again and get the following results. If the colors are Black, Red and White (and Green, if available,) the voltages will read as follows: B to R > 240V; B to W > 120V; R to W > 120V; W to G > zero V. For purposes of testing only, you should get the same voltages comparing a HOT wire to either neutral or ground (Green.) The White and Green will only share a terminal in the service entrance panel. (Different, though if the feed is a subpanel.) Please reply. Pinoke

No... Each T&P valve requires a 3/4" line and if you are required drain pans, they also must have separate lines.

Hello, I am a home maintenance guy. My name is Dave. I have encountered with my own hot water heater and others with the issue of leaking relief valves. The problem is very simple and the fix isn't difficult to fix yourself or something with a little plumbing ability. The problem is the pressure that builds up from the expansion of water as it is heated. After your water is turned off at your faucets and if you have nothing dripping, the water from the heater expands with no where to go but out the relief valve. If you have a faucet or toilet valve that seeps, then your relief valve won't leak, but of course you are wasting water energy and cash. You need to install an expansion tank at the hot water heater. You can find them at Lowes, HomeDepot, Amazon, EBay, etc. watch a YouTube video . Save yourself a lot of money and much easier on your pipes to have that excess water pressure that builds up. It can even damage your refrigerator water dispenser valve.