TP valve on Hot water heater. BAD???

1). At what water pressure should a T&P valve start to open?
There is about 80-85psi in the tank, when is starts to open.
When it does close, it seals tight.
2). Is there a way to know if is starting to go bad?
3). Do they go bad? Weak spring !
4). Are they easy to replace?
5). If I have to replace it what Spec's do I need to know when asking for a new one?

The TP is rated for 150 PSI at which pressure it should be wide open. In practice, if the pressure gets to anywhere above 110 or so, it is not unusual to have weeping.

80 PSI is the upper limit of what you should see in the house. 85 is too high. But we would not expect the TP to weep at that pressure. Do you have a regulator on the house pressure? Are you sure the pressure is only 85 when it leaks? In a closed system , the pressure can run up while the WH burner is on. It gradually drops back to normal pressure.

If it is opening at 85, it is bad and should be replaced, which is easy. They are screwed into the side or top of the tank.

Assuming we are talking about a "normal" household WH, the TP would be rated at 150 PSI, 200 to 212ºF. It also has a BTU rating, which must be higher than the listed BTU rating of your WH, which you will find on the label.

There are two "standard" TP available, short shank and long shank. It depends on whether yours is located on the top( short shank) or side ( long shank)

The PSI coming into my house is around 80-85 measured at the water spicket (awesome), but the T&P value was blowing water all over the cellar floor. We had an expansion tank installed at the WH years ago. Helped, but did not resolve problem. This weekend I installed a PRV off the main coming into the house. Also installed two PSI gauges, before and after the valve. The valve is set to 60-65 psi (a huge difference in pressure at the faucet and Shower head). I have a portable gauge off the bottom on the WH and it measured a high of 85psi when the T&P valve opened. Before installing the PRV it was not unusual to see a high at the WH of 100psi. This is why I was wondering if the T&P could go bad.
My T&P valve is located on the side of the WH near the top. I will ask for a long shank.

Another question. What should the normal temp of the hot water coming out of the WH be?

When you installed the PRV, you created a closed system. When the water heats it expands and the PRV prevents this expansion for being absorbed into the city water system. This causes the pressure in the water heater to rise very quickly and that's what is tripping the TP valve. You need an expansion tank in the supply line. It sounds like the TP valve is working properly.

Gary Please clarify: "You need an expansion tank in the supply line."
My previous posting stated that we had one installed years ago on the WH. I you stating that I have to have another one installed?

He said the gauge read 85 when thr TP opened, so expansion or not, it should not open at that pressure, and should be replaced

Expansion tanks go bad and can leak air. Have you checked yours to see if it is in good shape and still has any air pressure? Shut off the water and open a faucet prior to checking the pressure. Set the tank to around the normal working pressure of your system. If it was set too low previously, you overextended it and it is probably shot.

w1ljm said:

Gary Please clarify: "You need an expansion tank in the supply line."
My previous posting stated that we had one installed years ago on the WH. I you stating that I have to have another one installed?

Click to expand...

I basically answered this question a week or so ago when you first asked about how much pressure was normal. Your tank is either bad or is not properly inflated.

I did not mean to harp on this, but I was getting conflicting info. (JIMBO's reply, did make some sense). I do appreciate all the feed back from everyone. You can be sure that I will be investigating the expansion tank along with the T&P valve.