T &P valve opening constantly


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Old 01-07-08, 07:40 PM
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T &P valve opening constantly

I have two 40-gallon electric water heaters. Water trickles out of the overflow pipes continuously, one more than the other. It runs up quite a water bill.

After replacing the T&P valves this week, the trickle continues. I began looking at the water pressure regulator as the culprit, assuming it was allowing the pressure to be so high that the T&P valves were open most all the time.

I stuck a pressure guage on the washing machine hose bibb, the only working bibb I have. Immediately it hit the 100psi peg when opened. The guage would not move downward as I adjusted the pressure regulator downward even though the appearent pressure in the sink or tub was noticeably weak. If I turned on any other outlet when it was at 100psi, it would drop to 20 or 30, depending on the degree of drip, even down to zero. When I turn off the other outlet the guage would slowly move back up to 100psi.

The overflow never stopped completely, even with the supply to the water heater(s) cut off. Above 40-45 psi, it begins to trickle steadily and continues stronger as it moves back up toward 100psi.

There is something about this that I don't understand. What should I do ?
 
  #2  
Old 01-08-08, 03:49 AM
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Welcome to the forums! Are your water heaters zoned or are they tied in tandem? If in tandem, it would be a good idea to install an expansion tank above and between them. Certainly you don't want 100 psi slamming into your system. All your joints will be compromised unless you can get it back down to a constant 65 psi or so. As well, if your PRV is not adjusting properly, it may be crying for replacement. Check your temperature also. Too high a setting not only jeopardizes personal safety, it can cause the T&P to fail. Mid range setting is best.
 
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Old 01-08-08, 06:12 AM
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Thanks. No, they are not in tandem.One goes to one apartment, the other to an adjacent apartment. Both are on the same supply and meter.

How do I use the pressure guage? When I attach it to the hose bibb and turn on the bibb it should, if correct, be in the 65psi range. Should it stay at that reading if I open other faucets? In other words, what is the process by which I would arrive at the 65psi or any other reading?
 
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Old 01-08-08, 03:55 PM
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The water pressure will drop, although not appreciably, maybe down to 35 psi as long as the faucet is open. Once it is closed, the gauge should hop back to 65 psi ideally. And it is a good idea to allow this fluctuation in the supply line to ensure no air bubble and the prv is operating properly.
 
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Old 01-08-08, 05:27 PM
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Your PRV has a failed diaphragm. Classic sypmtoms. It tries to regulate when there is flow ( dual problem...diaphragm or springs stuck, so it can't actually maintain set pressure.) As soon as flow stops, street pressure passes by the diaphragm.

It is typical for TP valves to weep at any pressure over 100, and yours now probably has gunked up and should be replaced, after replacing the PRV.


The available range from almost any typical PRV is about 25 to 75, so when you see pressures higher than that, no adjustment is possible. It is just shot.
 
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Old 01-08-08, 08:16 PM
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Okay, friends. I'll try a new pressure reducing valve. Thanks. Dr Punchout.
 
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Old 01-10-08, 06:19 PM
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I just replaced the PRV, set it at 65 psi, and the new T&P valve on the new water heater installed a few days ago continues to allow a small stream of water to come out the overflow pipe. Temp is set at less than 125 F. Could the new T&P have gotten compromised so quickly? It is the devil to replace because within a few inches of the ceiling. More help needed.
Originally Posted by Dr. Punchout
Okay, friends. I'll try a new pressure reducing valve. Thanks. Dr Punchout.
Originally Posted by 594tough
Your PRV has a failed diaphragm. Classic sypmtoms. It tries to regulate when there is flow ( dual problem...diaphragm or springs stuck, so it can't actually maintain set pressure.) As soon as flow stops, street pressure passes by the diaphragm.

It is typical for TP valves to weep at any pressure over 100, and yours now probably has gunked up and should be replaced, after replacing the PRV.


The available range from almost any typical PRV is about 25 to 75, so when you see pressures higher than that, no adjustment is possible. It is just shot.
 
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Old 01-12-08, 06:40 AM
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I guess we should have talked also about this issue....expansion tank. Reviewing your post, I still think the PRV was for sure bad. But there is another issue. When water is heated, it expands. In a closed pipe system, that expansion has nowhere to go, and there result is a temporary rise in pressure, which can be a quite significant rise. Eventually, pipes cool down, a tap is opened, etc. and pressure returns to normal. An expansion tank attached on the cold water inlet pipe area of the WH prevents this temporary expansion from going so high that the TP valves weep.

You could check this by putting on your pressure gage...then run a lot of hot water, to the point that the heater turns on. Then shut the taps. and watch that gauge for several minutes as the tank heats back up.
 
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Old 01-13-08, 08:39 PM
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Originally Posted by 594tough
I guess we should have talked also about this issue....expansion tank. Reviewing your post, I still think the PRV was for sure bad. But there is another issue. When water is heated, it expands. In a closed pipe system, that expansion has nowhere to go, and there result is a temporary rise in pressure, which can be a quite significant rise. Eventually, pipes cool down, a tap is opened, etc. and pressure returns to normal. An expansion tank attached on the cold water inlet pipe area of the WH prevents this temporary expansion from going so high that the TP valves weep.

You could check this by putting on your pressure gage...then run a lot of hot water, to the point that the heater turns on. Then shut the taps. and watch that gauge for several minutes as the tank heats back up.
Okay, thank you. I'll try that. IF that is the problem, why is it just now showing up nine years after installation, I wonder.
I appreciate your help as this is stumping a number of local plumbers. Dr. Punchout.
 
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Old 01-13-08, 09:05 PM
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I'll offer a possible reason why it took several years for this problem to arise.

If you have large "air chambers" on your faucets (they would be inside the walls) then the trapped air in these pipes would act as an expansion tank. Over the years the trapped air is gradually absorbed by the water and the chambers have less capacity to absorb pressure increases due to thermal expansion.
 
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Old 01-14-08, 10:02 AM
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Originally Posted by Dr. Punchout
I have two 40-gallon electric water heaters. Water trickles out of the overflow pipes continuously, one more than the other. It runs up quite a water bill.

After replacing the T&P valves this week, the trickle continues. I began looking at the water pressure regulator as the culprit, assuming it was allowing the pressure to be so high that the T&P valves were open most all the time.

I stuck a pressure guage on the washing machine hose bibb, the only working bibb I have. Immediately it hit the 100psi peg when opened. The guage would not move downward as I adjusted the pressure regulator downward even though the appearent pressure in the sink or tub was noticeably weak. If I turned on any other outlet when it was at 100psi, it would drop to 20 or 30, depending on the degree of drip, even down to zero. When I turn off the other outlet the guage would slowly move back up to 100psi.

The overflow never stopped completely, even with the supply to the water heater(s) cut off. Above 40-45 psi, it begins to trickle steadily and continues stronger as it moves back up toward 100psi.

There is something about this that I don't understand. What should I do ?
Okay, I tried the test heat expansion as a cause of weeping T&P valve. I put pressure guage on hose bib at washing machine. It read 60 psi. I ran about 30 gallons out of the hot water side of the sink faucet. At 15 gallons the psi dropped to 45. When I turned faucet off psi went up to 52 and to 45psi when 18 gallons had run out (and the water was losing temp to the touch). I let it run to 30 gal. and shut it off. PSI went back up to 60 after two minutes, and it stayed there for the next 30 minutes when I stopped the test.
Something I forgot to mention: after I changed the PRV (which I agree must have been defective), one of the two T&P vlaves in question stopped weeping and has continued to stay closed. To review, I have two water heaters (#1 and #2)one for each of two efficiency apartments. Before I changed the PRV both were weeping. After I changed it, #2 T&P valve stopped. Also, just before I changed the PRV, the #1 heater was failing, so I changed it out for a new one with new T&P valve. At the same time I changed the T&P valve on #2.
Before I replaced the PRV, both were weeping. After, #2 stopped but #1 continues. It is this one that I did the thermal expansion test on just now and the one that continues to baffle me.
This makes me think the #1 T&P might be faulty, since #1 and #2 systems are coming off the same supply from the street and both were served by the PRV that I replaced. Assuming my test re thermal expansion was properly done.
Also, I was the general contractor on this house and don't recall air chambers on the faucets at installation.
Thanks for all the help. What now? Dr Punchout
 
 

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