Need help w/ new hot water heater

I just put in a brand new gas hot water heater and at first it appeared everything went smooth, then two hours after installing it, I saw a somewhat strong flow of water coming out of the T&P valve. I then ran back to Home Depot and bough a new T&P valve and even turned down the temperature to about 90 degrees. Then overnight I saw a lot of water came out of the new T&P valve once again.
After browsing through this group and doing some research, it appears I might have too much pressure coming from the public water. But I'm surprised because I never had this problem on my old hot water heater. Both of the valves are the same (I believe 170 PSI or 205 degrees)
A few questions: 1) Is there a possibility I could have a defective water heater? It's a 40 gallon GE 6year that I just purchased from Home Depot. I'm on my second T&P valve.
2) Why didn't I have this problem on my old hot water heater? (they use the same T&P Valve)
3) If this is the case, can I get away with just installing a pressure reducing valve, or will I need an expansion tank as well.
Thanks for any help!
Mike
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snipped-for-privacy@yahoo.com wrote:

The old T&P may have been stuck/off calibration, etc. This is not due to a bad heater.
Without having measured the street pressure, I can't say for sure if you need a PRV (regulator). If it's over 80psi, you need one.
And, if you install a PRV, you will need a thermal expansion tank.
http://www.amtrol.com/thermxtrol.htm
Jim
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that.
that will happen if you don't test them. Of course, then they can get stuck open...

if your pressure is over 60psi you ought to have reducing valve. Does your water system have any kind of backflow preventer? If so, you need an expansion valve anyhow; that is your current problem. FWIW, I put a pressure reducer valve in 2 years ago but no expansion tank. My pressure never goes up high enough to matter.
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Thanks Jim and Toller for your helpful response(s)
I just ran out to Home Depot and purchased a water pressure gauge (the kind that goes to the outside faucet) and I'm going to measure every location I can find! I suppose my old T&P valve was just old by the time the public water built up enough pressure to be an issue and now I have to install an expansion tank and/or PRV.
My problem is that my HWH inlet comes vertically from the room above and it looks like it's going to be hard if I have to make something horizontally and make room for an expansion tank. If I can put that right where the main comes in I should be alright. But if not, can I get away with just a PRV and where exactly does that have to go? Right before, or right after the HWH, or anywhere else? Toller you mentioned you have the PRV without the expansion tank, is there any drawback? Can I have an expansion tank without a PRV?
Also, what's the smallest size expansion tank I can get? Does it have to be horizontal too? Some of the bigger ones look to heavy to have it sideways, but I was hoping a small one might be able to go vertical (meaning the tank is sideways instead of directly on top)
Thanks for your help,
Mike
Toller wrote:

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snipped-for-privacy@yahoo.com wrote:

<SNIP>
http://www.zurn.com/pages/catalog.asp?ProductGroupID &OperationID The XT is perfect for 40 gallon and BigBox has them.
Put the PRV near where the service comes in. Pipe it so that the outside hose taps are *before* the PRV to maintain high pressure outside if you wish.
The exp tank can be hung downward (or upward) or sideways with support. Simply put a TEE in the Cold inlet line to the water heater, preferably after the shutoff valve.
A thermal exp tank is required by Code any time a PRV is installed. There *are* conditions where you may get away without one, but I would want to protect a new heater against unnecessary pressure buildup in any event.
Jim
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high the pressure maxs out at 85psi. Since that is more extreme than anything that could actually occur I feel comfortable without an expansion tank. (the PRV supposed will let water flow back if the house pressure exceeds street pressure, but street pressure is 90psi, so it is academic.)
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I went back to Home Deport and picked up a Pressure Reducer Valve. It's just above the HWH in the input/cold water. The funny thing is this has a dial thingy to turn to set the pressure so I am experimenting with that. It did start to leak at one time (a slight flow) so I still have to tweak it. If the pressure is unbearable I'll have to turn it all the way up and then install an expansion tank that I haven't tried yet.
Is there a correct way to adjust the Pressure reduce valve? I tightened it all the way and then backed it off one turn. I'll see how it goes overnight, I've got my fingers crossed!
Also, I put a pressure gauge to the outside faucet and it read 110 PSI - which is incredibly high! I should have ran the water first though, it's always high when I first turn it on.
Thanks,
Mike
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So after installing the pressure reducing valve (just above the water inlet and without an expansion tank) the pressure in my upstairs is unbearably low. I have the reducing valve turned in all the way and set to allow for the highest pressure. Is it possible that the valves come in ranges and perhaps I got the wrong one?
Any ideas?
Thanks,
Mike
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snipped-for-privacy@yahoo.com wrote:

Expansion Tank......Only answer to resolve the problem!!!
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snipped-for-privacy@yahoo.com wrote:

Screwed all the way in should produce 60psi or so, more than enough (usually).
Get your pressure gauge out and connect somewhere downstream of PRV. Perhaps a washing machine hookup. See what the regulated pressure drops to when water is used upstairs. Ideally, there will be little change.
Is it possible that a service valve is not fully open somewhere, restricting flow?
Jim PS Exp tank has no effect in this situation.
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I just went back to Home Depot and spoke to someone who knew what they were doing this time! Apparently the last one I bought was a pressure reducing valve for a boiler - NOT a hot water heater. That explains it as they're not suppose to go beyond 15psi. Now I got a new PRV that's a lot bigger and ranges from 50-75 PSI.. I'll hopefully get that in tonight and follow up.
Thanks again for your help!
Mike
Speedy Jim wrote:

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Okay - I'm finally making some kind of headway. I did put in the PVR and everything went well, except I did get a slight leak from the T&P overnight. This is consistent with Jim mentioning that I'll need an expansion tank to go along with it. I plan to do that shortly. The hardest problem is finding a place to keep the tank. I'll probably have to somehow run a pipe from my tiny "heater room" area to a crawl space. I'm assuming the expansion tank has to go between the PRV and the HWH inlet? I put the PRV just before the HWH so my room is limited, I'll have to move stuff around accordingly.
Thanks,
Mike
snipped-for-privacy@yahoo.com wrote:

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tank can go anywhere on cold water line, but cant be in a freezing area.........
the bladder inside with pre charged area allows the tanks watewr to expand and contract so your valve doesnt leak.
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