System losing pressure - Not sure where???

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twofer

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Jun 4, 2008
91
SLP Michigan
About a week ago I let my system sit idle for a couple days and eventually the storage temps got down into the 80's. When I went to start a fire I noticed that the pressure gauge on the return pipe to the boiler was reading 0psi. I figured that it was probably just due to the problems when the system was put and the expansion tanks precharge was too high. After correcting the precharge on the expansion tanks the system has always been 140-180° so when everything cooled down the water contracted and pressure went down to zero, or so I thought. I opened up the ball valve going to the fill (paranoid) and got the system back up to 12psi. The next time I went down to start a fire the system was back to 0psi and has been every time since then. Thinking that there must be a slow leak somewhere I spent last night going through the system but couldn't find any leaks. This is odd because the fill will run for a few minutes each time before it starts to get up to pressure which means there is a good amount of water going into the system.

A few odd things I've noticed is when the circulator for the water-to-air exchange kicks on the system pressure almost immediately begins to drop. Also, the system pressure last night started climbing into the 20's. This hasn't happened since I corrected the precharge in the expansion tanks. Another weird thing is that I cannot find any evidence that the PRV has opened up.

Do you guys have any ideas???? I am thoroughly confused.

Attached is a rough diagram of my system setup.
 

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Normal for pressure hot/cold/hot to fluctuate higher/lower/higher...

The air in your expansion tank will get warmer when the system is hot, and this increases pressure... when it cools, it decreases pressures. Even a small amount of air in the loops will warm and cool, causing pressure fluctuation.


twofer said:
About a week ago I let my system sit idle for a couple days and eventually the storage temps got down into the 80's. When I went to start a fire I noticed that the pressure gauge on the return pipe to the boiler was reading 0psi. I figured that it was probably just due to the problems when the system was put and the expansion tanks precharge was too high. After correcting the precharge on the expansion tanks the system has always been 140-180° so when everything cooled down the water contracted and pressure went down to zero, or so I thought. I opened up the ball valve going to the fill (paranoid) and got the system back up to 12psi. The next time I went down to start a fire the system was back to 0psi and has been every time since then. Thinking that there must be a slow leak somewhere I spent last night going through the system but couldn't find any leaks. This is odd because the fill will run for a few minutes each time before it starts to get up to pressure which means there is a good amount of water going into the system.

A few odd things I've noticed is when the circulator for the water-to-air exchange kicks on the system pressure almost immediately begins to drop. Also, the system pressure last night started climbing into the 20's. This hasn't happened since I corrected the precharge in the expansion tanks. Another weird thing is that I cannot find any evidence that the PRV has opened up.

Do you guys have any ideas???? I am thoroughly confused.

Attached is a rough diagram of my system setup.
Click to expand...
 
LeonMSPT said:
Normal for pressure hot/cold/hot to fluctuate higher/lower/higher...

The air in your expansion tank will get warmer when the system is hot, and this increases pressure... when it cools, it decreases pressures. Even a small amount of air in the loops will warm and cool, causing pressure fluctuation.


twofer said:
About a week ago I let my system sit idle for a couple days and eventually the storage temps got down into the 80's. When I went to start a fire I noticed that the pressure gauge on the return pipe to the boiler was reading 0psi. I figured that it was probably just due to the problems when the system was put and the expansion tanks precharge was too high. After correcting the precharge on the expansion tanks the system has always been 140-180° so when everything cooled down the water contracted and pressure went down to zero, or so I thought. I opened up the ball valve going to the fill (paranoid) and got the system back up to 12psi. The next time I went down to start a fire the system was back to 0psi and has been every time since then. Thinking that there must be a slow leak somewhere I spent last night going through the system but couldn't find any leaks. This is odd because the fill will run for a few minutes each time before it starts to get up to pressure which means there is a good amount of water going into the system.

A few odd things I've noticed is when the circulator for the water-to-air exchange kicks on the system pressure almost immediately begins to drop. Also, the system pressure last night started climbing into the 20's. This hasn't happened since I corrected the precharge in the expansion tanks. Another weird thing is that I cannot find any evidence that the PRV has opened up.

Do you guys have any ideas???? I am thoroughly confused.

Attached is a rough diagram of my system setup.
Click to expand...
Click to expand...

But is it normal to go back to 0psi? Because that's what my system has been doing every morning and night so far.
 
But is it normal to go back to 0psi? Because that's what my system has been doing every morning and night so far.[/quote]


Depends on a few things...

1. Location of check valves and circulators...

Picture a vertical loop with your wood boiler on one side and a check valve in the top of the loop. Now, add to that a loop representing your "heating system", with circulators. Now, picture the check valve closed, wood boiler down to room temperature and circulator not running. Circulating water in the heating system loop, may cause the pressure in the wood boiler loop to be at or near zero...
 
A few odd things I’ve noticed is when the circulator for the water-to-air exchange kicks on the system pressure almost immediately begins to drop. Also, the system pressure last night started climbing into the 20’s. This hasn’t happened since I corrected the precharge in the expansion tanks. Another weird thing is that I cannot find any evidence that the PRV has opened up.


Purged that heat exchanger well lately?? Air trapped in there will cool and contract, heat and expand, rapidly fluctuating the pressure in front of the pump, and behind it, because it's a loop.
 
But haven't you been adding water? Where is that going?

Any guess how much water? Unless it's leaking somewhere the only place I can see the water going is into the expansion tanks. But if the expansion tanks are becoming waterlogged you should be seeing higher pressures when the heat rises. And eventually, when the tanks get closer to completely waterlogged, the PRV will start blowing.

Any chance that your radiator is leaking but evaporating when it is hot and the fan is running. It might leak a lot of water you would never see that way but why is it not leaking all the time?
 
DaveBP said:
But haven't you been adding water? Where is that going?

Any guess how much water? Unless it's leaking somewhere the only place I can see the water going is into the expansion tanks. But if the expansion tanks are becoming waterlogged you should be seeing higher pressures when the heat rises. And eventually, when the tanks get closer to completely waterlogged, the PRV will start blowing.

Any chance that your radiator is leaking but evaporating when it is hot and the fan is running. It might leak a lot of water you would never see that way but why is it not leaking all the time?
Click to expand...

Exactly, I add water every time to bring the pressure back up to 12 psi. The next time I go to start a fire the pressure is back to zero. I have no idea where is it is going. Last night I tore apart the box around my storage tank looking for signs of a leak but couldn't find anything. Maybe it is evaporating but seeing how box is full of insulation you'd think that some of it would still be visible.

Not really sure but I can tell you that it is a 1/2" copper pipe coming directly off the well and that it runs for a few minutes each time. I am seeing higher pressures when the heat rises but I haven't found any evidence that the PRV has opened up. If the expansion tank was becoming water logged it would seem that the pressure would get too high and the PRV would open up.

Maybe the radiator is leaking but I can't see any signs that it is. What is confusing about this scenario is that the pressure will hold until the circ for the radiator comes on and then you can visibly see the pressure drop.

I am soooooooooooooo confused.
 
The pressure dropping when the radiator loops fills is a big clue. That indicates where the water is leaking. I would look very very closely at each piece of the radiator loop.

In my system, Which is basically similar to yours, I had a pressure drop when the system would cooled down. I traced it to a drain valve that would only leak when the system cooled down.

Keep hunting ...its leaking somewhere.
 
I hope you don't have this problem. This was happening to me when I had my Wood Gun. It turned out that the water was seeping out of the boiler walls through porosity caused by corrosion, into the log chamber when the boiler was operating and going out the stack as steam.
 
Last night I figured out what the problem was: failing expansion tank. This is confirmed by water coming out the air valve in the bottom and the PRV opening up last night as the system pressure got too high.

My theory is that the expansion tank was slowly failing and the water I kept adding to the system to get everything up to pressure was just going into the air space. The reason the pressure would immediately begin dropping when the circ for the water-air heat exchanger kicked on is because the heat was getting pulled out of the system. The water in the system would begin contracting and with the expansion tank not working correctly the pressure would slow drop until it was down to 0psi.

While I'm glad to have figured it out I am not scrambling to get a replacement expansion tank.
 
Glad you got it figured out. Here's an observation or two. You should always pump away from the point where the expansion tank is connected to the system for the sake of getting an accurate pressure reading and air elimination. If you can remodel your piping to do that as well as connecting your xpn tank(s) to the air scoop that will help eliminate some trouble in the future.
 
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