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Discussion Starter · #1 · (Edited)
So today we go on a call today for a relief valve dripping on on indirect water heater in a new house. We check the street pressure which is good, check the expansion tank on the cold side which is good so we change the relief valve and twenty minutes later it's dripping again.

I asked if we created a closed loop by installing a check valve on the hot side. My theory being that the check valve prevents any pressure building up on the hot side from reliving itself via the expansion tank no matter how high it builds. The mechanic said no, the heater won't build up enough pressure to make the valve leak, their must be something else wrong.

He based his diagnosis on two other strange things. The domestic hot was running almost ten degrees higher then it was set at. The second this is we usually run boilers at 160-180, this was at 195. We didn't install the boiler, it's a high efficancy job another company put in. He determined based on that that the coil must be leaking inside the water heater. If the coil was leaking wouldn't you have the domestic water (60psi) going into the boiler (12psi) blowing off the boilers relief valve, not the other way around though?

Now I'm not looking to go challenge the guy or anything. I'd like to know just this for my own knowledge and I ask here because he is the kind of guy who does not like explaining things. So should their be an expansion tank on the hot side with this setup? If not why is one not necessary? What about the coil thing, would the circulator or temperature difference make it leak from low pressure to high? .

 

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Chase Plumber
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Hot water expands, so therefor if the line got hot enough, it could burst, if the check is at the h/w tank on the hot side.

Check valve should be on the cold coming in BEFORE the expansion tank imo, that way it'll let the hot expand back through the tank if need be.


Just my 2 cents.
 

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I think your expansion tank is on the wrong side of the check valve not allowing pressure build up back into the main.
 

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What is the exp tk air pressure? What is the system water pressure? If the Air pressure is below the system water press, the water pressure could be dead heading almost like the Exp tk wasn't even installed. Also, where the recirc line ties into the cold, is there a check valve upstream of the recirc outlet back into the cold water?
 

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Always Something
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The check goes on the recirc line. You can do it that way too, but there should be one on the recirc line. The xtank is doing nothing unless there is a back flow preventer at the service entrance. If there is not a BF preventer than whoever put that X-tank there is not understanding how the system works. It's a volital situation as it is right now because there is nowhere for the pressure to go...so it's purging out the relief valve, as it should but that is a worst case situation....just plumbed wrong.
 

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Discussion Starter · #6 · (Edited)
What is the exp tk air pressure? What is the system water pressure? If the Air pressure is below the system water press, the water pressure could be dead heading almost like the Exp tk wasn't even installed. Also, where the recirc line ties into the cold, is there a check valve upstream of the recirc outlet back into the cold water?
Its an Amtrol ST-12. I just checked online at it seems they come pre=charged at 40 however we did not test the air bladder pressure. The water comming into the house is 56psi. So you're saying with this setup the expansion tank is not doing anything?
I am not sure what you are saying about the check valve upsteam. What I drew in that diagram is the how it is plumbed. Their are a few ball valves and drains not shown but no tees, check valves, etc. Originally it was installed without the check valve, the check was added later on to keep it from pumping the hot water through the cold side.

The check goes on the recirc line. You can do it that way too, but there should be one on the recirc line. The xtank is doing nothing unless there is a back flow preventer at the service entrance. If there is not a BF preventer than whoever put that X-tank there is not understanding how the system works. It's a volital situation as it is right now because there is nowhere for the pressure to go...so it's purging out the relief valve, as it should but that is a worst case situation....just plumbed wrong.
If the check valve is on the recirculating line and not the cold line what keeps the pump from pumping hot water into the cold side? Their is a back flow device out in the meter pit so the expansion tank is necessary


I just wanted to make sure I wasn't crazy here. He's saying it's dripping because the new water heater needs to be changed. I disagreed and said it needs a tank. I'm not in a position to argue with the guy though. So is this the proper way to install a recirculating line, just lacking an expansion tank, or it it totally wrong? If it's wrong does anyone have a picture/diagram of the right way to do it?
 

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residential service
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Its an Amtrol ST-12. I just checked online at it seems they come pre=charged at 40 however we did not test the air bladder pressure. The water comming into the house is 56psi. So you're saying with this setup the expansion tank is not doing anything?
I am not sure what you are saying about the check valve upsteam. What I drew in that diagram is the how it is plumbed. Their are a few ball valves and drains not shown but no tees, check valves, etc. Originally it was installed without the check valve, the check was added later on to keep it from pumping the hot water through the cold side.
If it is as you say according to the diagram then when the check was installed, the exp tank was completely cut off and rendered useless. Test the exp tank. If you get no pressure or if there is water present at the air valve when you put the gauge on it then replace the exp tank, relocate the check to the recirc line. Not sure what code you are on but the IPC calls for exp tank when there is a prv present in the system even if there is no form of check valve at the head of the system. Some prv's have built in bypasses up to 150 psi which is usually the upper pressure limit of the exp tank.
 

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So today we go on a call today for a relief valve dripping on on indirect water heater in a new house. We check the street pressure which is good, check the expansion tank on the cold side which is good so we change the relief valve and twenty minutes later it's dripping again.

I asked if we created a closed loop by installing a check valve on the hot side. My theory being that the check valve prevents any pressure building up on the hot side from reliving itself via the expansion tank no matter how high it builds. The mechanic said no, the heater won't build up enough pressure to make the valve leak, their must be something else wrong.

He based his diagnosis on two other strange things. The domestic hot was running almost ten degrees higher then it was set at. The second this is we usually run boilers at 160-180, this was at 195. We didn't install the boiler, it's a high efficancy job another company put in. He determined based on that that the coil must be leaking inside the water heater. If the coil was leaking wouldn't you have the domestic water (60psi) going into the boiler (12psi) blowing off the boilers relief valve, not the other way around though?

Now I'm not looking to go challenge the guy or anything. I'd like to know just this for my own knowledge and I ask here because he is the kind of guy who does not like explaining things. So should their be an expansion tank on the hot side with this setup? If not why is one not necessary? What about the coil thing, would the circulator or temperature difference make it leak from low pressure to high? .

He is absolutely wrong. I just recently replaced my own 40 gal electric water heater. Water heating doesn't get any more basic than this. When I did the install I had already used my last exp tank on another job the day before so I simply sweated in the tee and adapter and put a plug in the adapter until I could get the expansion tank. As soon as the tank came up to the factory set temp of 125, the t&p started weeping. I got the expansion tank, charged it to about 60 psi, installed it and the t&p has not moved since. I have also, in the past, in order to demonstrate to ho's their need for an exp tank, put a gauge on the wh drain and then ran hot water in a shower for 10 minutes. When you turn off the water, watch the gauge as it climbs. Sometimes it does it slowly sometimes it does it quickly. This is also a good way to test the t&P (which fails to open when it is supposed to a shocking percentage of the time) without manually operating the valve. I have seen them climb to 165 psi within 3 minutes and the t&p still didn't open.
 

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Plumber Manhattan Beach
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I am sure this was already said, the expansion tank is on the wrong side of the check, it is not doing anything to reduce expansion from the boiler.

I would move the expansion tank, not replace the coil or anything, there is not anything wrong with the unit, if it is running hotter, possibly a thermostate problem, but get the expansion under control first.
 

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WCP is right, if that Xtank is behind the check valve, it is doing absolutely no good. Yooz got a bomb on ya hands !!!
 

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So today we go on a call today for a relief valve dripping on on indirect water heater in a new house. We check the street pressure which is good, check the expansion tank on the cold side which is good so we change the relief valve and twenty minutes later it's dripping again.

I asked if we created a closed loop by installing a check valve on the hot side. My theory being that the check valve prevents any pressure building up on the hot side from reliving itself via the expansion tank no matter how high it builds. The mechanic said no, the heater won't build up enough pressure to make the valve leak, their must be something else wrong.

He based his diagnosis on two other strange things. The domestic hot was running almost ten degrees higher then it was set at. The second this is we usually run boilers at 160-180, this was at 195. We didn't install the boiler, it's a high efficancy job another company put in. He determined based on that that the coil must be leaking inside the water heater. If the coil was leaking wouldn't you have the domestic water (60psi) going into the boiler (12psi) blowing off the boilers relief valve, not the other way around though?

Now I'm not looking to go challenge the guy or anything. I'd like to know just this for my own knowledge and I ask here because he is the kind of guy who does not like explaining things. So should their be an expansion tank on the hot side with this setup? If not why is one not necessary? What about the coil thing, would the circulator or temperature difference make it leak from low pressure to high? .




This may be caused by a pinhole leak in the indirect water heater. I have seen it a few times myself. Depending on how bad it is leaking with the street pressure usually being around 80 it doesnt take long for a leak like that to build up enough pressure to kick out that relief valve.
 

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This could be casue by one of two things. Either the system has two check valves and you cant get any expansion or the indirect heater has a pinhole leak in it. Obviously if the system is new the check valve is most liekly the problem, however if it is fairly old than a pinhole leak with doesnt take long to build enough pressure to set off the relief valve. You can check this by shutting off the feed to the tank. Good luck
 

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Yep. The check valve is in the wrong place. And its really quite simple to understand. Where it is now creates a closed loop system in the hot water piping. As the water heats up, pressure builds up and since the check valve by design keeps water from flowing backwards (i.e. into the cold system), you'll never get a build up of pressure at the expansion tank.

Here in the Houston area, we don't typically install expansion tanks on residential water heaters, but are required to on boilers and I believe all commercial systems. The reason is because to prevent hot water from entering the cold water system, you must install a check valve. However as mentioned earlier, this creates a closed loop in the hot system hence the need for the expansion tank.

We don't install them on residential systems because there typically isn't a problem with hot water entering the cold system. And since there isn't a check valve, the system isn't closed and any increase in pressure can be absorbed on the cold side and more to the point, the entire public distribution system. And yes, I understand that brings up a whole nuther set of problems when you consider backflow. Personally, I think all plumbing systems connected to any public system should have backflow prevention (i.e. RPZ). But for now, this is how we do things and it seems to be perfectly fine.
 

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If the check valve is on the recirculating line and not the cold line what keeps the pump from pumping hot water into the cold side?

The circulator is pulling water from the bathrooms and pushing it back into the tank. The water entering the tank, which is already full, has to go somewhere, so water gets drawn back up the hot side. Water follows the path of least resistance.
I think thats why it wont go into the cold side. But then again I could be wrong.

We also put the check valve on the recirc line. If you didnt have one on the recirc the water could go up the recirc instead of down it.
 

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Discussion Starter · #18 ·
The circulator is pulling water from the bathrooms and pushing it back into the tank. The water entering the tank, which is already full, has to go somewhere, so water gets drawn back up the hot side. Water follows the path of least resistance.
I think thats why it wont go into the cold side. But then again I could be wrong.

We also put the check valve on the recirc line. If you didnt have one on the recirc the water could go up the recirc instead of down it.
I'm not arguing with you here, I'm just trying to understand something I don't fully grasp.
Water follows the path of least resistance, that's obvious enough. If someone turns on the cold water without the check valve where it is won't the pump wind up forcing hot water up the cold side line? It seems to me without a check valve in that spot you have a major hot/cold cross connection. Does someone have a picture or diagram of a properly set up re-circulating line handy?
 

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you really do just need to move your expansion tank.

the check valve is fine, I always use a check valve on my recir lines, you need to have 1 no matter what.

Thanks WCP, I think that one has been beaten a few times...None the less, I agree on the x-tank.
 
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