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Pressure Relief Valve - Is it needed

11 years ago

The Hot water heater has one along with a expansion tank. There is another pressure relief valve that was original to the house (built 15 years ago.) The expansion tank was added with a replacement hot water heater about 5 years ago. Is the this second pressure relief valve needed, or can I remove it?

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Comments (8)

bus_driver
11 years ago
The one on the water heater is required by many codes and is the most crucial one in my opinion. Not sure which you mean by the "second" one.
User
11 years ago
Some places require a separate PRV if supply pressure is high. Best to ask a local plumber or look up local code requirements.
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One of my pet peeve's has been people who post on forums seeking assistance, asking for help, but then, once they find the answers necessary to solve their problem, don't bother reporting the solution leaving the string the dangling! It’s as though they don't realize that a public forum is not solely for their use or benefit but also (arguably more so) to serve others that will be searching for the same information about the same issue, possibly, for many years to come. I realize we’re all more motivated to write when pressured by those problems that need solving but, considering the time spent and efforts made by others kind enough to generously offer their assistance, taking a few minutes to post a solution once found is the least one can do. I didn't get back to this as soon as I would've liked to but I’ll not be one of those people so back to my story and its exciting conclusion. They've recently been replacing the main gas lines in our area. I didn't immediately see any connection but it seemed too much of a coincidence that these previously nonexistent leaks and drips should randomly begin to occur very near the same time that construction began. I talked to one of the guys which lead to talking to some of the other guys which eventually lead to speaking with the guy in the water department. What I learned is that the waterline in this area is, more or less, a loop supplied on both ends. In the event that, while excavating to install the gas lines, some sort of damage is done to the water line that necessitates an emergency shut off, they shut off the supply on one in advance so that, if needed, they could immediately stop it by shutting off the other side. This apparently caused an increase in the water pressure of the loop. He (the guy from the water department) opened up the other end and our pressure here dropped from 148 down to 120, apparently still considerably higher than normal or is desirable, but low enough to make a difference. All leaks have stopped. So, to answer my own original questions, higher than what is considered normal water pressure —but not necessarily in excess of its stated psi rating —will or can cause flow from a pressure relief valve. Also (I was previously unaware of this) other fittings, valves etc. throughout the house plumbing are only designed to withstand up to a certain pressure. As for me, I suppose I still need to install a pressure reducing valve but I don’t need to install one today. In the meantime, I may be able to pressure wash the house without a pressure washer!
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dave6768
Original Author
11 years ago
I understand the one on the hot water heater. There is another pressure relief valve that was installed when the house was built. It's this other valve that's in question.

Yesterday, I disovered that valve was leaking. Discovered that the pressure reducing valve coming into the house was shot and repalced it. The pressure in the house was 90 psi. After replacing the PRV, this other pressure relief valve was still leaking (but not as much.) So, I have to replace or remove the offending valve.
User
11 years ago
Dave,

Sounds like you may be confused between a PRV (pressure reducing valve or pressure regulating valve) installed at the water service entrance and the T&P (temp & pressure) relief valve installed on the WH.

A PRV is installed at the service entrance to lower the street pressure to an acceptable PSI for the houses plumbing. Depending on water conditions they go bad and need to be replaced from time to time. They are usually set to around 60 psi.

A T&P relief valve on the WH is a safety device and is installed so the water heater doesn't explode if pressure problems arise. When these T&P valves leak they MUST be replaced and with EXACTLY the same specification part or maybe... BOOM.

The expansion tank should be check annually when you drain your water heater. You do drain your WH annually don't you?. To do that you put an air gauge on the air valve. If the bladder has failed then you'll get water out of the air valve. If you don't get water then you must drain all the water from the tank, which usually requires removal, and the air bladder needs to be pressurized to what the water pressure is when the tank is empty.
dave6768
Original Author
11 years ago
Nope...no confusion. There are three valves. The pressure regulator on the line coming into the house, the T&P relief valve on the water heater and a third pressure relief valve that has the vent line running outside. This third valve was leaking...I replaced it today. My question is do I need this third valve. If not, I'll unscrew the new one and put in a plug.
User
11 years ago
Is the third valve a T&P valve? If it is they are cheap and there's nothing wrong with having two. Might be code in your area to have two.
brickeyee
11 years ago
"Is the third valve a T&P valve? "

Probably cheaper and easier to find than a pressure only valve since every water heater requires one.

PRVs typically turn the house into a partially sealed system since they do not allow back flow.

This post was edited by brickeyee on Mon, Apr 15, 13 at 10:13
dave6768
Original Author
11 years ago
It's just pressure and I found one at the second hardware store I went to for about $8. Rather than take the risk that it was code, I just replaced it. It was easy enough to do. Next time, It will only take 30 minutes to swap instead of 1.5 hours. :-)

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