lol i know i know - i'm just trying to a) figure out how to make it operate at a lower pressure; b) figure out if my relief valve is correct (sounds like 40 is probably ok - but I don't want to operate at that)
Burnham goes overpressure in the AM
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Fitter30
Well-Known Member
Need to check out the ex tank. 40 gallons of water that temp is raised 70° expands 1.9 gallons
John Gayewski
In the Trades
I don't want to jump in on this post and make it worse. But one thing at a time. Forget the relief. The expansion tank is the main suspect. Your fill valve should be set at 15 that's what will set your system pressure as it will keep adding water until it gets to 15psi.
The expansion tank is just a place for swelled up water to go. It's a soft spot. It needs to be working and set 1psi or so above the fill valve.
The expansion tank is just a place for swelled up water to go. It's a soft spot. It needs to be working and set 1psi or so above the fill valve.
Thanks John. I replaced this expansion tank in 2019 - could it be bad already?
I checked with another gauge, and that one shows the pressure at around 10psi under the boiler as well.
I suspect my system would run better with a bigger expansion tank, but all the pipes around it are set so that it won't take one....
John Gayewski
In the Trades
If your expansion tank is undersized which I imagine it is, because someone put the wrong relief valve on there, then it would/could break almost immediately.
You think my relief should really be a 30 - with a MAWP of 50? Concerns me that it's a shoddy install - I don't want this thing to be a safety risk.
GrumpyPlumber
Licensed Grump
I was going to say that myself, but, oh wait, I did.
John Gayewski
In the Trades
Boilers have regulations. 30 is the regulation. I can imagine an installer or service person saying "man this relief keeps dripping, it can't be anything I did wrong (sizing the expansion tank wrong), it must be this valve is the wrong one. LOL
Bannerman
Well-Known Member
Cold water will expand when heated so the expansion tank's purpose is to provide the physical space to absorb the additional volume of the expanded water when heated. Since a liquid cannot be compressed, when the expansion tank is too small or is waterlogged, there will be insufficient space available to absorb the additional water volume so the water pressure will rise and the pressure relief valve will seep to reduce the pressure.
Your water feed regulator should not be maintaining pressure within the system as the system is a closed loop. Since it is a closed loop, the only time new water should be added is when there is a leak, or when refilling the system after maintenance/modification. With closed loop systems, anti-oxidation and anti-corrosion chemicals will be typically utilized so draining and refilling will be normally minimized.
If the water supply valve that feeds the pressure reducing valve is to always remain open, then the reducing valve's pressure setting should be calibrated 2-3 psi lower than the expected pressure whenever the system is shut off and the water is cold. In this manner, the reducing valve should open to add more water automatically only if there is a major pressure loss, usually as a result of a broken pipe or fitting. The pressure reducing fill valve will be normally equipped with a lever to override the pressure setting to allow manually filling the system to a higher pressure.
Since it is the expansion tank that maintains system pressure, the expansion tank should not be completely empty when the water is cold as the tank's air precharge pressing against the diaphragm will need to supply constant pressure against the water.
When the pressure tank is correctly sized and is not waterlogged, the pressure variance between a cold and hot system will normally be only a few psi.
Your water feed regulator should not be maintaining pressure within the system as the system is a closed loop. Since it is a closed loop, the only time new water should be added is when there is a leak, or when refilling the system after maintenance/modification. With closed loop systems, anti-oxidation and anti-corrosion chemicals will be typically utilized so draining and refilling will be normally minimized.
If the water supply valve that feeds the pressure reducing valve is to always remain open, then the reducing valve's pressure setting should be calibrated 2-3 psi lower than the expected pressure whenever the system is shut off and the water is cold. In this manner, the reducing valve should open to add more water automatically only if there is a major pressure loss, usually as a result of a broken pipe or fitting. The pressure reducing fill valve will be normally equipped with a lever to override the pressure setting to allow manually filling the system to a higher pressure.
Since it is the expansion tank that maintains system pressure, the expansion tank should not be completely empty when the water is cold as the tank's air precharge pressing against the diaphragm will need to supply constant pressure against the water.
When the pressure tank is correctly sized and is not waterlogged, the pressure variance between a cold and hot system will normally be only a few psi.
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John Gayewski
In the Trades
I agree mostly and in principle. Except that an expansion tank cannot set or change the pressure in the system. It can only react to the pressure set by the fill valve/prv.
If you set your expansion tank at 2 psi and install it, your system pressure will not be 2psi, because your fill valve WILL pressurize the system is its own set pressure.
Bannerman
Well-Known Member
John, I think you misunderstand.
I said to set the pressure reducing fill valve to 2-3 psi lower than the intended cold water pressure. This should then reduce the potential for the valve to add more water whenever the boiler is turned off and the water is constricted while cold.
I also said with an adequately sized expansion tank, the pressure differential from when the water is hot and cold should be only a few psi, not 20 psi.
If the expansion tank only contained 2 psi air precharge, there would be insufficient air to be compressed, thereby resulting in the X tank filling too much so as to become mostly waterlogged when the boiler and piping is filled with water up to operating pressure.
I said to set the pressure reducing fill valve to 2-3 psi lower than the intended cold water pressure. This should then reduce the potential for the valve to add more water whenever the boiler is turned off and the water is constricted while cold.
I also said with an adequately sized expansion tank, the pressure differential from when the water is hot and cold should be only a few psi, not 20 psi.
If the expansion tank only contained 2 psi air precharge, there would be insufficient air to be compressed, thereby resulting in the X tank filling too much so as to become mostly waterlogged when the boiler and piping is filled with water up to operating pressure.
I think I follow by now.
Here's what you should know: I didn't size the relief or the expansion tank. The size of the expansion tank is limited by clearance. It just won't fit a bigger one.
Here's what I did
1) Turned the boiler off and pulled some water out to let it come back to cold pressure (right at 15 PSI)
2) Added some air to the expansion tank - both gauges were reading that it was very low. (brought it to 14 PSI)
3) For good measure, I upped the min temp from 120 to 140 or so so that it won't work as hard in the morning
4) I'm going to watch it like a hawk over the next 24 hours, and if this doesn't work (and I don't think it will), I'll call a professional
Let me know if any of that sounds crazy, otherwise I'll report back the results
Here's what you should know: I didn't size the relief or the expansion tank. The size of the expansion tank is limited by clearance. It just won't fit a bigger one.
Here's what I did
1) Turned the boiler off and pulled some water out to let it come back to cold pressure (right at 15 PSI)
2) Added some air to the expansion tank - both gauges were reading that it was very low. (brought it to 14 PSI)
3) For good measure, I upped the min temp from 120 to 140 or so so that it won't work as hard in the morning
4) I'm going to watch it like a hawk over the next 24 hours, and if this doesn't work (and I don't think it will), I'll call a professional
Let me know if any of that sounds crazy, otherwise I'll report back the results
Not crazy, except I maybe did not totally understand #3. Are you saying that your boiler maintains a minimum water temperature, even when the thermostat(s) don't call for heat?
I think it will be better.
If you wanted to have a bigger thermal expansion tank, I think you can pipe to a tank that is farther. They even make big tanks intended to sit on the floor; those would normally be for bigger buildings I think.
I think it will be better.
If you wanted to have a bigger thermal expansion tank, I think you can pipe to a tank that is farther. They even make big tanks intended to sit on the floor; those would normally be for bigger buildings I think.
Thanks!
wrt 3 - yes, there is a 'min' setting, that I believe I had dropped because it was supposed to make the boiler more efficient at a lower number. The thing is that it appears to be one factor that makes the system run harder in the AM, when folks are getting up, running water, all four zones of heat are pulling heat out of the system.
On the expansion tank...thanks very much for your note there - that's part of why i want to call a pro. Just rip the bandaid off and hear my options on relief / expansion size.
Bannerman
Well-Known Member
The only way the air pressure with the expansion tank should be different than the system water pressure would be if you closed the isolation valve between the tank and boiler, then drained the tank completely of water so there was No Pressure remaining in the tank's water chamber.
If you checked the tank's air pressure while the valve between it and the boiler remained open, the air pressure should have been identical to the water pressure within the boiler.
GrumpyPlumber
Licensed Grump
Your boiler is not supposed to exceed 30 psi for a 2K sq/ft home, just because the label states "max psi" doesn't mean that's operating pressure -
Hence my "Maximum water temp 250f" - Please, don't." comment.
Increasing the low temp might mitigate it temporarily, but will cause the boiler to short cycle and effect efficiency.
One person here, John Gayewski, stated the most likely reason you'd have a 40 psi relief, whoever installed your expansion tank probably realized it was undersized and opted for the less expensive 40psi valve band-aid over replacing the tank.
At the point that you're altering boiler settings I start to get nervous, altering temps won't fix this problem, might be time to get a heat/plumbing guy out to do this.
Hence my "Maximum water temp 250f" - Please, don't." comment.
Increasing the low temp might mitigate it temporarily, but will cause the boiler to short cycle and effect efficiency.
One person here, John Gayewski, stated the most likely reason you'd have a 40 psi relief, whoever installed your expansion tank probably realized it was undersized and opted for the less expensive 40psi valve band-aid over replacing the tank.
At the point that you're altering boiler settings I start to get nervous, altering temps won't fix this problem, might be time to get a heat/plumbing guy out to do this.
Does this low temperature setting cause the boiler to not let the water drop below that limit during the whole heating season, or is it something else?
Hi Grumpy - don't worry, I'm leaning toward the same and watching it closely. Part of the underlying issue is .... was the original install bad , if so I probably need to call someone else in. (Install was under previous owner)
After doing some reading, the measurements above appear to indicate that the aquastat is letting the system run too long. Could that cause the issue?
What was supposed to happen:
-Start off at min 140 F
-Diff was set to (~17)
-Shut off at 157
What did happen:
-Shut off at 175 (max)
Points to the aquastat being the problem, right? Assume that no matter how the tank is sized, etc..... letting the system run too long will inevitably cause pressure problems?
After doing some reading, the measurements above appear to indicate that the aquastat is letting the system run too long. Could that cause the issue?
What was supposed to happen:
-Start off at min 140 F
-Diff was set to (~17)
-Shut off at 157
What did happen:
-Shut off at 175 (max)
Points to the aquastat being the problem, right? Assume that no matter how the tank is sized, etc..... letting the system run too long will inevitably cause pressure problems?
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