Too Much Pressure in Water Heater?

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Disney1984

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I have a 50 Gallon State water heater attached to hydronic heating system in my home attic. I had the water heater professionally installed by a plumber about 5 years ago. The unit had a problem with the 150 PSI tp valve blowing immediately after the installation. The plumber was frustrated and confused at why it was blowing. He added an expansion tank just to be safe. He also installed another new tp valve and its worked fine for 5 years. About six months ago I noticed the tp valve blowing again. I've had a couple of plumbers come out and they can't figure out what the problem is. They checked the expansion tank and it isn't full of water and appears to be OK. I performed my own investigation. Water pressure at a hose bib outside of the house is a constant 60-65 PSI. I placed a pressure gauge on the water heater at the drain bib as well. I discovered that pressure at the water heater bib would reach 140 PSI towards the end of the water being heated after someone took a shower right before the burner would kick down. The 140 PSI slowly drops after the burner turns down. The PSI at the outside hose bib remained a constant 60-65 PSI. The tp valve starts leaking a small, but steady stream at 140 PSI. It's obvious to me that the tp valve is bad because it shouldn't blow until 150 PSI, but I'm being told the internal pressure of the water heater should never get that high. I called the Tech line at State Water Heaters and told them of my problem. The temperature setting on the water heater isn't to hot and is set at 120 degrees. It was at 125 degrees. State says the internal pressure of the water heater shouldn't get over 80 PSI. The pressure gets to 140 PSI without the hydronic house heater being on. The weird thing is the water heater pressure recently stopped jumping to 140 PSI and stayed at 65-70 PSI through the heating cycle. It was fine for a about 3 weeks and the problem has started up again. Should the internal pressure of the water heater get up to 140 PSI? The manufacturer says no. Does anyone have any idea what could be going on here?
 

John Gayewski

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No the pressure should never get that high. Something is wrong. The first thing that is wrong is your water heater is hooked to your hydronic heating system.

The only way to figure it out is to look at the setup and see how it's piped.
 

Reach4

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The unit had a problem with the 150 PSI tp valve blowing immediately after the installation.

I assume you are exaggerating, and the pressure only rises when you stop using water, and the WH heats water. I further assume that water only dribbles out of the T&P valve rather than "blowing".


Water heaters in systems fed via a check valve need a thermal expansion tank. The elevated pressure comes when you use hot water, stop using water, and the water heater heats the new colder water.

Do you have a check valve, or a non-bypass PRV in line with the path to the WH, but after the outside spigot water tees off?
 
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Sylvan

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No the pressure should never get that high. Something is wrong. The first thing that is wrong is your water heater is hooked to your hydronic heating system.

The only way to figure it out is to look at the setup and see how it's piped.
501.2 Water Heater as Space Heater

Where a combination potable water heating and space heating system requires water for space heating at temperatures higher than 140°F (60°C), a master thermostatic mixing valve complying with ASSE 1017 shall be provided to limit the water supplied to the potable hot water distribution system to a temperature of 140°F (60°C) or less. The potability of the water shall be maintained throughout the system.
 

John Gayewski

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501.2 Water Heater as Space Heater

Where a combination potable water heating and space heating system requires water for space heating at temperatures higher than 140°F (60°C), a master thermostatic mixing valve complying with ASSE 1017 shall be provided to limit the water supplied to the potable hot water distribution system to a temperature of 140°F (60°C) or less. The potability of the water shall be maintained throughout the system.
This is illegal in a great many jurisdictions mainly because of the last sentence in your snippet. This is a type of system that should be avoided and is generally frowned upon by professionals even where it legal.
 

Disney1984

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First, I would like to say that I really appreciate everyone's comments. I'm not a plumber, but I fix a lot of things around my home and I'm technically inclined. I've avoided working on my water heater in the past because of potential safety issues, but I can't seem to get answers on what the problem is from my local plumbers, and they keep charging me to just look at the unit.

My home is about 25 years old, and the builder designed it with an Apollo hydronic system. My home was built with a 50-gallon State water heater, and it worked great for 20 years until it started leaking. The two hydronic lines come off the side of the water heater. It's been like that since day 1 and its always worked out fine. The replacement State water heater installed 5 years ago is almost identical to the original, but its ultra-low NOx.

The last plumber that came out was in his 20's and seemed a little inexperienced. He checked my expansion tank and said it was fine. I decided to check it myself last night and it was extremely heavy. I'm concluding that it must be filled with water because it fills so heavy. This is evidence of a failed expansion tank, right? Could this be the reason the internal pressure of the water heater is reaching 140 PSI at times?
 

Disney1984

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I think this is a one-way check valve that's in-line on the water supply to the water heater. The plumber that installed my current water heater added it. It wasn't there when I took possession of the house. I would expect to see an arrow pointing one direction, but I don't see any. I don't have enough experience with these. Is this a one-way check valve and could it be contributing to the problem? Thanks in advance.

IMG_1995_50.jpg
 

Disney1984

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Thank you Reach4. My current expansion tank measures 7 inches wide. Should I replace it with the same size expansion tank or go larger? My tp valve is leaking at 140 psi and is rated at 150 psi. It's not really blowing. It's more of a steady light medium flow of water that leaks out for 3-4 minutes until the water heater pressure goes back under 140 PSI. I'm thinking I should just leave it alone, since it's still working and it's probably not good for the tank to be at 140 PSI anyways. I'm thinking I shouldn't go to the trouble to replace the tp valve unless its start releasing water at lower PSI's. What are your thoughts on this?

As I said earlier, this has been going on for about 6 months. Do you think the integrity of my water heater is still good with pressures getting up to 140 PSI? Has the tp valve done its job and the integrity of the water heater should be fine? Especially with it releasing early at 140 PSI?

As a side note, you guys have been great. I've been working with local plumbers and the State tech phone line and I get told different things that conflict each other. I'm so happy I decided to reach out in this forum.
 

Disney1984

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I appreciate your response Terry. Do you still think I may still need a PRV after my recent posts? Do you think I need a PRV in addition to the tp valve?
 

John Gayewski

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Change the expansion tank. There should be very little water in it at any one time no harm can come from over sizing an expansion tank. The inside of your heater has a lining which is glass or some other coating. When you get high pressure like that it flexes the tank and ruins the lining which will rot your tank much much faster than it should. The check valve is only one peice of the puzzle. We would need to know how it's all arranged. It really seems like a bad or water logged expansion tank.
 

Terry

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I appreciate your response Terry. Do you still think I may still need a PRV after my recent posts? Do you think I need a PRV in addition to the tp valve?
A T&P valve releases if the water is too hot and if the pressure is too high.
It has nothing to do with the regulation of pressure in the system. If the pressure is high, then you need a pressure reducer.
I doubt very much that the pressure reducer in your home is located where it does anything for the rest of the home. You might want to remove a washer hose and check the static pressure there too.

Expansion tanks don't control pressure. A "PRV" is used to regulate pressure.
All plumbing codes require a PRV if the pressure is over 80 PSI

index.php
 
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John Gayewski

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A T&P valve releases if the water is too hot and if the pressure is too high.
It has nothing to do with the regulation of pressure in the system. If the pressure is high, then you need a pressure reducer.
I doubt very much that the pressure reducer in your home is located where it does anything for the rest of the home. You might want to remove a washer hose and check the static pressure there too.

Expansion tanks don't control pressure. A "PRV" is used to regulate pressure.
All plumbing codes require a PRV if the pressure is over 80 PSI

index.php
The pressure is 60 to 65psi. It's the hot water that's gaining pressure, likley backing up against the check valve. A prv won't regulate that unless it has a built in bypass. We really need to see how this is set up. These systems should be open and one long loop which causes other problems and A prv will not let pressure, built up from the heated water, push back into the city water supply which is how we do it here. If there is A prv it needs a properly sized expansion tank set at the correct pressure to relieve the system.
 
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wwhitney

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You might want to remove a washer hose and check the static pressure there too.
It was easy to miss in the OP as it is a wall of text, but he stated "The PSI at the outside hose bib remained a constant 60-65 PSI."

Expansion tanks don't control pressure. A "PRV" is used to regulate pressure.
Yes for water supply pressure. But the expansion tank is used to control pressure due to water volume expansion from a heat source after a check valve, which is apparently the issue the OP has, a failed expansion tank.

Cheers, Wayne
 

Terry

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I did not "miss" that the front hosebib is a steady 60-65 PSI

Has anyone taken the pressure at the water heater, with the heat turned off?
It may be that the front bib has a reducer on it for irrigation purposes.
In all my years of plumbing, I've never had cold water to a water heater, heated up to 125 degrees ever get over 90 PSI
Something else is the problem, turn the heat off to the the water heater, let it cool overnight, take a pressure check in the morning.

"The unit had a problem with the 150 PSI tp valve blowing immediately after the installation. The plumber was frustrated and confused at why it was blowing."

Of course a lot of you are assuming the home was plumbed correctly. I get that. I don't think it was.
 

wwhitney

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I did not "miss" that the front hosebib is a steady 60-65 PSI
OK, then I misunderstood your suggestion.

In all my years of plumbing, I've never had cold water to a water heater, heated up to 125 degrees ever get over 90 PSI
I have no direct experience, as locally water heaters don't have any check valves between them and the municipal supply, but isn't it expected that with a check valve and no functioning expansion tank, the water heater would cause the T&P valve to open when heating up a cold tank?

Cheers, Wayne
 

Terry

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OK, then I misunderstood your suggestion.


I have no direct experience, as locally water heaters don't have any check valves between them and the municipal supply, but isn't it expected that with a check valve and no functioning expansion tank, the water heater would cause the T&P valve to open when heating up a cold tank?

Cheers, Wayne
Not when starting at 65 degrees.
Most homes where I'm at are closed systems now. It's not the heating of the water that little bit, it's something else.
And that's why the installing plumber was confused.
 

wwhitney

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Not when starting at 65 degrees.
Well, now I'm confused, because I thought that was the whole reason that expansion tanks are required whenever a water heater is behind a check valve.

Water at 60F has a density of 999.07 grams/L, while at 120F it has a density of 988.70 grams/L per https://www.usgs.gov/special-topics/water-science-school/science/water-density That means it heating it from 60F to 120F will cause an expansion of 1.05%, or half a gallon for a 50 gallon water heater. Without an expansion tank, where does that half gallon of water go?

Cheers, Wayne
 
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