T & P valve on water heater blowing

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Scott Baxla

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A friend's water system has been working fine for at least 10 years. This week the T & P valve on the hot water heater started leaking. (Mounted on the top of the tank - don't have to drain tank to replace it.) My first suspicion was bad T & P release valve, so I replaced it. The new one did the same thing.

Then I went to the city water supply side suspecting a pressure spike (her house is at the bottom of a hill). There is a pressure reducer valve where the water line enters the basement. Printed on the side of this reducer valve is max incoming water pressure of 300 psi, reduced to between 25 and 75 psi. I installed a gauge on the house side of the pressure reducer valve and the gauge seems to settle around 45 psi, but for some reason goes to 0 when any faucet is turned on and that doesn't make sense to me - it wouldn't come out of the upstairs faucet it the psi was 0. I'm doubting the accuracy of the new gauge. Anyway, I'm assuming average working psi of 45.

Next I went back to the water heater. There is a check valve (mounted vertically) on the incoming cold water line and a ball valve shut off between the check and the water heater. There is a Tee to a 4.4 gal expansion tank mounted between that incoming shut off and the water heater. There is also a shut off on the outgoing hot water line.

So the next thing I did was replace the expansion tank. Depressing the air valve spewed black slime water. With an auto tire gauge the precharge on the new expansion tank registered 45 psi. Perfect? (matching incoming water pressure.) When I removed the old expansion tank and drained the water out of the water side there was still significant water in it - on the other side of the diaphram. The tank was definately bad. The previous install of the diaphram expansion tank was vertical with water coming in top and air admittance valve on bottom. (Tank supported on a special shelf for it.) When I replaced it I reversed it - water in the bottom and air admittance valve on top. And I put the old T & P valve back on since the new one did the same thing and there was no appearance of corrosion on the old one. We turned the system back on and after a few minutes the T & P release started leaking water again.

I had to leave her house for an appointment and afterwards was conversing with the friend on the phone and walking her through diagnostic steps on the phone. Power to the water heater was already off. I had her shut off the outgoing and incoming water, and open the T & P valve - eliminating all water back pressure on the Expansion tank. and check the pressure on the expansion tank. It was down to 25 psi from previous rounds of testing the pressure when the T & P was leaking - must have drained significant pressure out of expansion tank. Knowing the current tank pressure @ 25, with the power turned off (no heat being produced) I instructed her to close the T & P, open the hot and cold lines to the house. With back pressure from the water now, the expansion tank immediately read 45 psi (this must be the working pressure of the cold water coming in - and that gauge over by the PRV must be reading okay). Then after less than a minute 50, then 75. I told her to quit checking it and wait. The T & P started leaking again in 3 -5 minutes and I had her check the pressure again and it was up to 139psi (not sure how accurate the electronic tire gauge is). So the tank was building pressure (quickly) with the power shut off and heat not being produced. This baffles me. The T & P "should be" blowing at that pressure - so I'm not thinking the old pressure release valve is faulty - its doing what its supposed to do. Why is the tank building pressure? I'm not there to verify that there is no power coming to the tank, but regardless, it was working fine for 10 years, and even if the power was on now, it should not build enough pressure to pop the release? Why is the pressure building now and it was not before the expansion tank went bad. Does the expansion tank just not work with the water coming in the bottom of it? That wouldn't make much sense to me either - there is still a diaphram with an air cushion to absorb pressure increase from water heating. And blowing at 139 PSI? Sure seems like we're risking blowing all the pex hot water lines in the house. Amazingly the flapper style check valve was keeping that pressure from going into the cold side - the gauge at the incoming water line still stayed around 45 when the expansion tank was reading 139.

Suggestions?
 
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jadnashua

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PRVs can leak, allowing the pressure to rise. Also, 300psi is very high, and MIGHT exceed the capacity of a single PRV to drop it to useable (code compliant) level without using two of them in series.
 

Scott Baxla

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Thanks for checking in jadnashua. I'm not seeing evidence that the PRV is leaking. The gauge I just installed on the house side of the PRV has never risen above 50 psi. The 300psi is just the number on the side of the PRV as the max incoming pressure for this PRV - not what the incoming city water pressure actually is. The house is over 60 years old and prior to about 20 years ago when the plumbing got totally re done it did not even have a PRV. I'm not thinking the city water line pressure would ever get up past the capacity of the PRV without blowing the city lines. The gauge I installed over beside the PRV does not increase when the pressure is increasing at the water heater. It appears that the check valve between the water heater and the cold water supply is keeping the pressure out - even though its just a flapper style check valve and not a spring loaded one. And the water coming out of the upstairs faucet is not coming out like a pressure washer, which is what I'd expect if it got up to 139 psi. The 139 psi reading came from the expansion tank air admittance valve using an automotive tire gauge - on the water heater side of the check valve - not from the house cold water supply on the other side of the check valve.
 

Fitter30

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Gallon capacity of water heater and hot water temp. Take a couple of pic of it.
Set ex tank at 60 lbs. If water pressure was over 80 lbs toilets cloths washer and dishwasher would be hammering when the solinoids would open and close.Drain valve work on heater put a gage on that. Prv usually have their own check built in.
 
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Scott Baxla

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Thanks for joining the threa Fitter 30. I've attached pics of 1) the PRV/gauge/filter at incoming water line to the house, 2) the plumbing configuration at the water heater, 3) the temp setting at just over 125 ( she has a toddler granddaughter that she doesn't want to risk scalding), and 4) the id plate on the water heater showing 50 gallons. None of these things have changed from 1 week ago when everything was working fine for 10+ years. Another interesting note on the expansion tank: from the black gook in the old expansion tank (manganese?) - filling the air side of the diaphram in the expansion tank and clogging the air admittance valve so we can't get it to drain, it would not appear that the expansion tank just failed this week, but the system was still working fine. The old expansion tank had a date of 2005 on it. (I believe the water heater and pop off valve are newer than that.)

Because there is no hot water, the dishwasher and clothes washer have not been operated in the last few days - since the problem arose. No hammering in toilets noted, and the water coming out of the tap seems normal - not like a pressure washer which is what I would expect if the house pressure was 140psi. I didn't follow the comment: "drain valve work on heater, put a gage on that." I've not opened the drain valve at all, we're bleeding off pressure by tripping the pop off valve - its in the top of the tank and we can leave the tank full.

I was thinking of pumping up the expansion tank to 75, but I'll follow your recommendation to try 60.

Update this morning. We've verified that the power is off at the water heater. The water in the tank is still warm after a few days, but no heat is being added to the tank - definately none added in last 12 hours. The how water tank should be static - not increasing in pressure. When we went through diagnostic efforts this morning - the same thing we did yesterday: 1) Isolated hot water heater from house by closing ball valves on hot and cold. 2) Open pop off valve to relieve any water pressure being exerted on the pressure tank. 3) Check pressure in the expansion tank and its now down to 17psi from the bleed off by checking it with a tire gauge. 4) Close the pop off and open the lines to the house to get the water heater back "online". 5) by checking with the tire gauge, within a few minutes the pressure at the expansion tank rose to 150 psi - which is the blow off setting on the pop off valve, and the pop off valve opened and started leaking water, and immediately dropped a few pounds to 140 but kept leaking, which seems normal. There is no heat being added to the hot water tank - the power is off. Why in the world would the pressure increase to 150 psi? The gauge over at the incoming water to the house still never goes above 50.
 

Attachments

  • incoming water supply.pdf
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  • tank configuration.pdf
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  • Temp setting.pdf
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  • Water Heater Plate.pdf
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Reach4

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Black gunk may be deteriorated diaphragm material.

You have a pressure gauge before your PRV. What does that read when you measure 170 psi at the thermal expansion tank?

I would also get a garden hose thread pressure gauge, and mount that at your WH drain temporarily. I am wondering if your air pressure gauge is accurate.

Your PRV has a screen that can normally be cleaned. The way your PRV is mounted, that cleaning will not be possible. That is not related to your symptom however.
 

Scott Baxla

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Thanks Reach4. Maybe the gunk is diaphram material. When I screwed the fitting off the top of the old expansion tank it had a black crust in it - I thought the crusty nature seemed manganese like, but I'm not familiar enough to know, I've just heard manganese is black. And it doesn't seem like its any part of the issue at hand. However the condition of the old expansion tank suggests to me that its been dead for some time and that did not happen in the last week when the pop of valve started blowing - the city must be having a pressure problem. I could be wrong on that, but if I'm right, then the "closed" system was working just fine without the expansion tank by using the pex lines in the house as the expansion tank.

The Pressure gauge in that picture is actually after the PRV. Flow is from Sch 80 fitting at bottom, to PRV, to Shut off valve, to gauge, to filter. That gauge is in theory measuring the water pressure in the house, and fluctuates from 0 to 50psi.

This morning after my last post, with the hot water tank isolated - no water going into the hot water pipes in the house, we verified that the hot water pipes had no pressure - no outflow at faucets. Then with the hot water tank isolated we released pressure from the hot water tank pop off valve. 5 minutes later, opened the pop off valve again, and nothing was released - therefore the hot water tank is not contributing any increase in pressure. We then opened only the cold water supply coming in to the hot water heater. When we did this, the gauge at the PRV read 0 psi, and stayed there for a few minutes (pressure relieved at the gauge to send it to the water heater). We could hear noise in the expansion tank at the water heater - as in building pressure in the tank. After about 3 minutes we tested the pressure at the expansion tank and read 110 psi on the tire gauge, while the gauge at the PRV started slowly increasing from 0 at this point. At about 5 minutes, the pop off started releasing water at the hot water tank. We tested the pressure at the expansion tank again with the tire gauge and it was 145psi - the pop off should be releasing water. We then read the gauge at the PRV and it was reading 35 and climbing slowly. This seems to confirm 1) The increasing pressure that is blowing the pop off valve is coming from the cold water supply, and 2) that gauge that was just installed at the PRV is faulty/ dramatically innacurate. (Recommendations on a quality gauge?) We're getting our parts from Home Depot and Lowes, which I'm sure are not the highest quality parts.

I'm currently thinking that the PRV is not doing its job, and considering replacing it, but its pricey - it would be good to know that it's faulty and doesn't just need cleaned. I'll have to uninstall it to get to the screen ports to clean it. Somehow in my mind I'm thinking if there were clogged screens then it would not allow pressure to go through - thereby reducing the pressure on the house side, not increasing it. Is this an inaccurate assumption? While doing this I'll swap places with the shut off and the PRV so we don't have to turn it off at the street to clean the PRV - it will always have to be removed to clean it where it is mounted in the cabinet that its in or the sliding door won't close. Or some crazy loop to move the PRV off to the right and still be able to get the filter off.

So... experience on cleaning the screen in the PRV decreasing the pressure on the house side? PRV's just go bad and need replaced every 10 - 20 years? The home owner has found info online about kits to rebuild PRV's so they must regularly wear out. Our PRV is a Wilkens Model 600 manufactured in 06/06. There was a thought that the PRV is mounted backwards, I've not looked at that, but if it has an internal check valve, then it wouldn't work at all. Certainly it seems like a better gauge would tell us what its actually doing, but the pop off valve seems to be saying that the incoming pressure is just too high. When I had the pop off valve off, it was relatively clean, not heavily crusted up with deposits.
 

Terry

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PRV's are not a forever thing. The internals can go bad, and I've also seen them somewhat blocked by debrie inside where the screen is. I've had them allow too high a pressure and sometimes not enough flow.

Most plumbers when they go out on a service call, can bring a new PRV and install the new one if there aren't parts handy on the job. Nobody wants a two trip job for something basic like that. And finding parts for something very old can be interesting.
 

Fitter30

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50 gallons of water raising the temp 70° water expands 2.5 gallons 50° to 120°
4.4 gallon should be good for a 80 gallon tank. Measure at clothes washer if tank valve doesn't work out. Swing check in vertical up flow might not close all the time. Spring check is the.proper check. First pic looks like 1/2" pex? With the brass 90° ( ell) and a filter wouldn't be surprised by a 10 lb pressure drop.
 
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Scott Baxla

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PRV's are not a forever thing. The internals can go bad, and I've also seen them somewhat blocked by debrie inside where the screen is. I've had them allow too high a pressure and sometimes not enough flow.

Most plumbers when they go out on a service call, can bring a new PRV and install the new one if there aren't parts handy on the job. Nobody wants a two trip job for something basic like that. And finding parts for something very old can be interesting.
Thanks Terry. This is reinforcement that its our PRV. I'm not a plumber but I'll be the one replacing it. I've actually done all the work on replacing all of the supply and drain in her house - significant experience for a DIY'er but not plumber level.
 

Scott Baxla

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50 gallons of water raising the temp 70° water expands 2.5 gallons 50° to 120°
4.4 gallon should be good for a 80 gallon tank. Measure at clothes washer if tank valve doesn't work out. Swing check in vertical up flow might not close all the time. Spring check is the.proper check.
Thanks Fitter30. That confirms that the expansion tank should be adequate, so our issue is somewhere else, and I think we're zeroing in on the PRV.
 

Reach4

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If you dribble water in the house, and close the red-handled valve, how quickly does the pressure rise at the pressure gauge? That takes the WH out of the picture.

This is not to say that if it takes some amount, such as 60 minutes, I would be able to give good analysis. But if it is 10 seconds, that would condemn the PRV.

I have no relevant experience, but the idea of the cash-acme pressure reducing valve eb25 models seems interesting. One piece to unscrew, giving access to the screen, or to replace the whole works, seems interesting. There are a lot of choices. https://www.supplyhouse.com/Pressure-Reducing-Valves-17082000
 

Scott Baxla

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If you dribble water in the house, and close the red-handled valve, how quickly does the pressure rise at the pressure gauge? That takes the WH out of the picture.

This is not to say that if it takes some amount, such as 60 minutes, I would be able to give good analysis. But if it is 10 seconds, that would condemn the PRV.

I have no relevant experience, but the idea of the cash-acme pressure reducing valve eb25 models seems interesting. One piece to unscrew, giving access to the screen, or to replace the whole works, seems interesting. There are a lot of choices. https://www.supplyhouse.com/Pressure-Reducing-Valves-17082000
I think that red handle you are referring to is at the PRV. There are also red handles at the Water heater, but in either case, closing either of those valves will take the water heater out of the picture. We've not tried the one at the PRV valve yet, only the other one by the water heater - which leaves all the pressure build up in the entire house cold water piping system to affect the gauge at PRV. This has been taking 3-5 minutes for the gauge to start registering again and get to its static working pressure which that gauge is saying is 45 psi but I'm thinking it should actually be reading 150 - 180psi (since the water heater pop off blows at 150psi and at that point the gauge at the PRV reads 35, but stops climbing around 45. . I see what you are saying by shutting off the one right there near the PRV - shutting off the entire house and isolating just the PRV. The repressure timing would be really short since it only has about 2' of pex and the water filter to pressure up. I'll try that when I get over there - about to walk out the door and won't have access to the computer for a while.
 

Reach4

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I was referring to the red handle at E. Yes, closing that valve takes the WH out of the picture. If the PRV leaks, the pressure would rise pretty quickly with that valve closed.

Usually people do not route outside water thru the cartridge filter, and often they don't route outside water thru the PRV. If your outside water tees off before the PRV, that would be a handy place to measure the pressure before the PRV.

If redoing a lot, consider putting the yellow-handled valve before the PRV.

img_7.jpg
 
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Jeff H Young

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if your pressure goes to 139 in a few minutes or even hours without the water heater on youve got high pressure coming in and a bad PRV .
 

Scott Baxla

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Thanks everyone for all of your comments. The issue seems to be resolved. It was the PRV. Seems crazy that the a city supply is over 150psi - that could do some damage. My confusion mostly revolved around having installed a new gauge just after the PRV, specifically to monitor what it was doing and that gauge not working properly. The suggestions for the bib mount pressure gauge were helpful. I'll look into Terry's Ashcroft gauge. I did rework the filter box with the new PRV and moved the shut off prior to the PRV now that I know PRV's go bad. The new PRV did not have the clean out port, but I installed it in a way that if it ever gets replaced again the clean out port would be accessible. If I can get a decent gauge it will be clear when it goes bad (probably at least 10 years from now...) Interesting comment about not running outside water through PRV or filter first, but the piping is not easily accessible. Seems like it would be interesting to be able to check pre PRV pressure just to know, but I guess bottom line is that it only matters what's happening after that. That filter only gets changed every few years when an inside pressure drop is noticable though - she probably doesn't use all that much water outside.
 
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