Scott Baxla
New Member
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?
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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