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 Water Heater TPR Mystery & Questions
Author: jepalan (SD)

Getting about 8oz of water from TPR every few days from less-than-2yr-old water heater.

I put a cup under the TPR discharge, and it stays bone dry, then about 1/2 to 1 cup of water shows up all at once. It is NOT slowly dripping. Seems to happen at end of heating cycle, but have not caught it in the act.

Some questions have come up as I investigate the cause.

House is 23yrs old. Replaced WH twice.
Current WH is 40 gal Rheem installed 1.5 yrs ago.
City adopted 2009 UPC so a 2-gal "T-5" Amtrol expansion tank was installed with the last WH. Never had e-tank before.

I will add some pics below.

I measured water pressure at outside hose bib (96psi) and at WH drain tap (98psi)
Expansion tank air valve measures 96psi, but I have not isolated it to see true pre-charge pressure yet.
Let a little air out and no water from expansion tank.
Hot water temperature from tap nearest heater is 100 deg F.

I know code says WP must be 80psi or less. Per code I believe a regulator needs to be installed.

Live in upper midwest and incoming water is VERY cold this time of year.

My theory is that tank cannot absorb thermal expansion near end of heating cycle - either b/c it is not pre-charged correctly, or b/c our house pressure is so high (or both).

Obviously we need to take care of the incoming pressure first.

Questions:
- See picture below. Where/how do I install the PRV? I think it needs to go between shut-off & meter, but no room.
- Am I missing anything regarding the spurt of water from TPR?
- Should I just get house pressure taken care of first and see if it takes care of TPR spurt?



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 Re: Water Heater TPR Mystery & Questions
Author: stuckinlodi (MO)

96 psi is some pretty strong water pressure. Since you didn't have a expansion tank before I'm wondering why you didn't have a problem with TPR leakage before this when you didn't have an expansion tank. Did the city do something recently that increased the water pressure, was the pressure lower in years past?

Anyway, you will likely need to install a pressure reducing valve, or a bigger expansion tank [last part is joke]. We'll see what the licensed plumbers around here have to say.

With pressure like that the firefighters in your town had better put an extra man or two on the firehoses.



Edited 3 times.

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 Re: Water Heater TPR Mystery & Questions
Author: steve (CA)

I'd put the PRV on the house side of the meter. With the water turned off and pressure bled, match the exp. tank pressure to the new house pressure.

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 Re: Water Heater TPR Mystery & Questions
Author: PlumberLoren (CA)

Steve is correct. Install the PRV above the tee to the sprinkler between the check valve.

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 Re: Water Heater TPR Mystery & Questions
Author: jepalan (SD)

Thanks for the replies. Thought I would provide an update...

Some of the mystery is starting to unravel...

I've been monitoring heating cycle after wife takes a bath. Pressure rises right at end of cycle to around 140~145 psi and TPR spurt may/may not occur. When cycle is done, pressure returns to 96~98 psi after a tap is opened.

It turns out that to meet current code, the check valve and expansion tank were installed along with the new WH 2 years ago. So prior to that our system was open to the source, then we became a closed system when the new WH was installed 2 yrs ago.

Remaining question is whether anyone bothered to check incoming pressure when they closed & inspected the system. I have a call in to city inspector that signed off on the job. There may actually be a PRV at the street feed that just needs adjusting or replacing.

If not, I will be adding one and adjusting the expansion tank pre-charge.

Thanks again.



Edited 1 times.

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 Re: Water Heater TPR Mystery & Questions
Author: PlumberLoren (CA)

If you have a pressure reducing valve in your system, verify that it is working by installing a pressure gauge from the big box store that reads up to 200 psi on a hose bib. You may have a leaking diaphragm rubber in the PRV. (quite common) Determine what brand PRV you have. Home Depot sometimes has rebuild kits for Wilkins valves, but check and see what you have then go to the local plumbing supply and purchase the kit. They are relatively easy to install if you have the proper tools. Some take a large i.e. 1 1/4" socket wrench to disassemble the valve and install the new kit. If you are not fairly mechanically endowed, call your local plumber for this job. You are dealing with potable water and want it done right. Good luck.

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 Re: Water Heater TPR Mystery & Questions
Author: jepalan (SD)

Quote

Author: PlumberLoren (CA)
If you have a pressure reducing valve in your system, verify that it is working by installing a pressure gauge from the big box store that reads up to 200 psi on a hose bib. You may have a leaking diaphragm rubber in the PRV. (quite common) Determine what brand PRV you have. Home Depot sometimes has rebuild kits for Wilkins valves, but check and see what you have then go to the local plumbing supply and purchase the kit. They are relatively easy to install if you have the proper tools. Some take a large i.e. 1 1/4" socket wrench to disassemble the valve and install the new kit. If you are not fairly mechanically endowed, call your local plumber for this job. You are dealing with potable water and want it done right. Good luck.


Thanks for the reply, I spoke with city inspector - there is NO PRV in my system.

The current plan is to have a professional plumber install a new PRV, then recalibrate the precharge on the expansion tank and see how it goes.

FWIW - inspector confirmed the city *has* tweaked pressures recently and they are seeing other issues in my area.



Edited 1 times.

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 Re: Water Heater TPR Mystery & Questions
Author: stuckinlodi (MO)

If the city has bumped up the water pressure by 10-15psi they are going to get calls from people that are now having leaks that never had them before. Our town went thru that, they connected to a new water treatment facility and everyone's pressure increased, which is not always a good thing.

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 Re: Water Heater TPR Mystery & Questions
Author: jepalan (SD)

Quote

Author: stuckinlodi (MO)
If the city has bumped up the water pressure by 10-15psi they are going to get calls from people that are now having leaks that never had them before. Our town went thru that, they connected to a new water treatment facility and everyone's pressure increased, which is not always a good thing.


Completely agree. The city inspector was careful with his words but he certainly seems to support the idea that some sort of public notice should be issued in certain neighborhoods. He even mentioned that they are so slammed with new construction inspections they rarely take time to measure pressures. If someone's heater explodes city might be liable for damage/injury.

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