I'm at my wits end on this one.

We recently installed a new Whirlpool water heater, and it frequently discharges a few drops of water out of the T&P relief valve. Our old heater did the same thing.

After doing some research online and finding our water pressure was too high, we purchased a Watts water pressure regulator and installed it on the main coming into our home. I also purchased a Watts pressure gauge that tracks not only the current pressure, but also the highest spike while attached.

I hooked the gauge to the drain outlet on the water heater and left it on overnight. The highest reading was 150psi. I'm assuming that I need to install a thermal expansion tank on the water heater to correct this problem.

The thing that baffles me is this... I adjusted the pressure regulator yesterday because we weren't happy with the water pressure while taking showers, etc. It is supposed to regulate water within 25 to 75psi. I turned it all the way open and got a reading of 70psi at the hose bibb on the back of my house.

I left the gauge attached to the bibb overnight and this morning had a maximum reading of 150psi and a current reading of 100psi. After taking a shower, the water pressure at the bibb was 60psi. Does this mean that pressure is building up within my closed system because of the water heater? Would this problem be alleviated by the installation of a thermal expansion tank?

Thanks a lot!

It sure would! Sounds like you are set correctly at 60 PSI but as the water heats it also expands jumping your PSI up to 150. This much pressure puts the fittings and faucets under a strain and should be repaired as soon as possible.
Purchase a expansion tank and install it on the cold water supply to the water heater. Now the added pressure has someplace to expand to. Good luck, Tom

An expansion tank is not the answer. Your pressure relief valve is leaking (short circuiting the pressure regulating mechanism) across the inlet and outlet. Very common problem. Take the pressure relief valve back to where you bought it and hope you can get a good one.

Dondhdh,

You responded to 2 1/2 years old post check the date in left upper corner, I believe this post is closed by now,Thanks.

John

John

Hi Donhdh

I'm afraid that I strongly disagree with you on that one... ;)

Clearly with the increases in pressure that we see described above you have to wonder why we are getting such high numbers, right? The only time we see this kind of phenomenon, especially associated with an old water heater and T&P valve and now the new heater and T&P valve, is when we have a CLOSED SYSTEM (due to check valves, backflow preventers, pressure regulators, etc. in the water system). When there is a closed system there is no place for the hot water to expand when it heats so you can see these large fluctuations and periodic dripping of the T&P valve to try to balance things out a bit.

Installing a new T&P is a good idea, but to resolve the issue permanantly an expansion tank is definitely recommended... see image below.

Questions? Let me know, OK?

Mark

PS: You said, "Your pressure relief valve is leaking (short circuiting the pressure regulating mechanism) across the inlet and outlet."... what does that mean? Thanks...

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"PS: You said, "Your pressure relief valve is leaking (short circuiting the pressure regulating mechanism) across the inlet and outlet."...what does that mean? Thanks..."

Mass, I wondered the same thing. I just thought my ignorance was showing.

I'm looking forward to the explanation... ;)

Dond did a time shift and went back 2.5 years to when this was posted, he's long gone and probably won't explain

Dondhdh posted (post #3) yesterday @ 5:16 PM... ;)

Hopefully, he'll be back to explain what he meant!

I may have answered this twice, so if I did, I apologize. What I was trying to say is that one should suspect the pressure regulator 1st before going out and buying an expansion tank. I agree that in some rarer cases an expansion tank may be warranted but most times, at least in California, the problem is more likely a failed pressure regulator. Here's why.

The pressure regulator valve (PRV) should open up and let water pass if downstream pressure is less than say 60 psi and to close if the downstream pressure is at or greater than 60 psi. And therein lies the problem. What if it doesn't completely close? Maybe, just like many shut off valves leak across the inlet to outlet(what I called short circuit)~so can a pressure relief valve. Both valves have the job of stopping water leaking from a higher pressure inlet to a lower pressure outlet.

In a closed system such as we have with our home plumbing, if the pressure relief valve leaks, the outlet pressure will gradually (depending on severity of leak) increase until the outlet pressure reaches the inlet pressure. No expansion tank will stop this.

Thus before you spend money buying an expansion tank, check to see if your PRV leaks. Once you've determined the outlet pressure is too high, go to a faucet and let out just a bit of water. Make sure not to let out so much water as to turn on the water heater. Hence you will have eliminated the thermal expansion effect. Let out just enough water to bring down the outlet pressure to 50 or 60 psi. Now watch and see if the pressure gradually increases. It may take 1 minute or 10 minutes, depending on the severity of the leak. If the pressure increases within this time and the water heater did not turn on, it indicates the PRV is leaking.

The PRV makers sell a repair kit for PRV's designed to stop this leaking. It is similar to a repair kit you can buy for a shut off valve. New o-rings, etc. The PRV makers suggest you inspect and check your PRV once a year for proper operation. I think one would be surprised at how many failed PRV's are out there and the homeowner doesn't even know.

And this post remains 2.5 years old. We appreciate the info but this is pretty much out of date

I posted the original question that started this thread, and I wanted to let everyone know that I took Tom's advice and installed an expansion tank. It DID fix the problem. I had forgotten about this ordeal until someone posted another answer and I was notified via email. Thanks for the great advice, Tom!

I posted the original question and had completely forgotten about it until I just received an email saying there were new answers. Tom's advice to install a thermal expansion tank worked like a charm. No more leaks! Thanks, Tom!

Tom is not here right now due to a medical issue but I will try to pass this onto him. Thanks for clarifying

Don, thanks for the answer. It did make sense. However, the person said his pressure was going up to 150psi. It's hard to imagine a water system with that much pressure, which would have to be the case if your PRV was simply leaking. Do they get that high (water system pressure)?