The pressure relief valve started leaking. I replaced it, but did not fix. Went to change thermostats and elements and found tank full of sediment, so I replaced the water heater. New one leaks from PRV as well. Input pressure at around 90psi. Upper element set at 130 degrees. Bottom at 125 degrees. Any ideas? I have a plumber friend indicating I need an expansion tank. Didn't need one the last 15 years. Spoke to a city employee as well who indicated nothing has changed with the water pressure.

You need to install a pressure regulator before the ball valve where the water enters your home and set it to 60 PSI is what I recommend. If you have copper water lines throughout your home, a lower pressure setting will save water but also reduce wear on the pipes. It is critical that the pressure relief valve functions. I try to stay away from Pressure Tanks as it is just another device to wear out and needs maintenance.

I agree. I don't have room for an expansion tank either. You indicate to install BEFORE the shut off valve. Any particular reason it cannot be installed AFTER the shut off valve instead?

If you install a pressure reducing valve, you create a closed system. If you are already having problems, you may find that a PRV does not solve the problem. It's not designed to solve that problem. Read the instructions for the PRV and you may find a potable water expansion tank is required. Position the PRV in such a way that valves can be shut to service or replace the PRV.

As I indicated I do not have an expansion tank on my system. I have my Pressure Regulator set to 60 PSI and in the event that it fails,(because it eventually will) I also have pressure relief a valve set to 80 psi attached to a tee on a hose bib connection. I actually have two of these installed in case one of them fails. Some will say this is over kill but I do not want my copper lines to exceed 80 PSI.

The fact that you get away with that may be more of a function of the extent of your piping. The OP may also be able to get away with it. If not, he'll know the answer.

That came out of my head wrong. Install the ball valve before the Pressure Regulator so you can maintain the Pressure Regulator and control water coming into the home. Hope this helps.

You do realize, don't you, that if the pressure exceeds 80 psi, and is not controlled by an expansion tank, your pressure relief valves will actuate every time and discharge water.

I don't understand your thinking. Read my reply above. I have no such problems and again I would not have an expansion tank in my potable water system.

Something must be taking up the excess pressure. If you put a pressure gauge on and watch it after someone takes a shower (as the water heater is firing) you'll see it climb. Some people can get away with a PRV and no expansion tank, but lot of others get a dripping TPR.

If your relief valves are NOT discharging, then the pressure is not exceeding 80 psi, and therefore you would probably NOT require an expansion tank.

I replaced my old electric hwt with a new tank and the new t and p valve leaks, nothing changed in the house, but the tank. The House pressure is 40 psi and the temp settings are at the factory settings.(140F) I could install an expansion tank, but my question is why did the old tank work without leaking and the new tank T&P leaks.