Fluctuating Pressure - Have Tried Many Things - Need More Ideas [SOLVED!!]

AllieEm

Hello all!

I have been searching the previous posts on this site for about a week now and have tried many ideas posted to others. Here is my issue.

Hot Water Oil Burner - pressure checked by an external gauge installed which holds at about 5 to 10 lbs. When heat starts climbing from 140 to 180, the pressure rises with it until it hits 30 psi. At that time the release valve works and dribbles water into the bucket.

I have replaced the expansion tank this fall which appears to have worked for a few months. It is still without water in it and holds pressure at 12 psi. Changed the air release valve above it a few days ago and that didn't seem to make at difference. (At that time, removed the exchange tank again and double checked it).

Tried shutting off the intake water for over a day and that didn't show any changes. On occasion I have found and released air in the baseboard heaters, but not a great amount. I have checked all the lines and items on the furnace for signs of leaking/leak evaporation which there are none.

I am at a loss to figure out where to turn next before having to call in someone who might end up just as lost as I am since the consensus seems to always point to the expansion tank. I hate paying someone to repeat what I have already tried.

So, I thought I would try here in order to get more than one person's opinion on what I might need to look at next. It is a very old furnace, but when serviced last winter I was told that it was still running efficiently and strong.

Any other thoughts out there that might cause the pressure to rise when it is actively heating? Once it is at 180 degrees it drops back down to between 5 and 12 psi.

Thank you!!

Jamie Hall

Do I understand you to say that it holds a constant -- and low -- pressure once it is up to temperature? I will say that 5 to 10 psi static for a hot water system strikes me as low...

Something is really weird there...

STEVEusaPA

We're going to need pictures, close up and the whole system.
Do you also use your boiler for domestic hot water?
If not, the only 3 causes.
-Air
-Failed bladder tank (make sure there isn't a closed valve between the system and the tank).
-Water feed leaking by, even when closed.
I would lean toward the first 2 because pressure rises when the temperature goes up. However, I've never seen boiler pressure drop when the temperature was up (unless the relief valve tripped), so I wonder about the relationship between the circulator, the boiler and the expansion tank. Does the pressure change when the circulator comes on or off?

If you do have an internal coil, a leaking coil could be introducing street pressure water into your boiler.

Unless the boiler and all the radiation are at the same elevation, 5 psi is too low.

Mike

Everything is pointing towards the xpansion tank. A new tank was installed, back in the fall. Why? Is the new tank the same size? If you turn off the burner for a hour or two, does the system pressure rise? I'm thinking the water feed valve is leaking by, and or the pressure gauge is out of calibration at low pressure.

delta T

Check the connection to the expansion tank, there is a chance that the connection is clogged with rust and gunk and not allowing the x tank to 'see' the system. Does it connect to the bottom of an air scoop?

Other things to check:
1. Make sure the charge is correct on the expansion tank (should be checked when the tank is not connected to the system, should be = to your static cold fill pressure, usually 12-15 psi)
2. What kind of pump do you have and where is it in the system? (pics will help with this)

AllieEm

Thanks for all your replies! I am going to take the photos now.

AllieEm

EBEBRATT-Ed

Are you 100% shure the valve between the expansion tank and the system is open? It could be broken internally

AllieEm

STEVEusaPA said:

We're going to need pictures, close up and the whole system.
Do you also use your boiler for domestic hot water?
If not, the only 3 causes.
-Air
-Failed bladder tank (make sure there isn't a closed valve between the system and the tank).
-Water feed leaking by, even when closed.
I would lean toward the first 2 because pressure rises when the temperature goes up. However, I've never seen boiler pressure drop when the temperature was up (unless the relief valve tripped), so I wonder about the relationship between the circulator, the boiler and the expansion tank. Does the pressure change when the circulator comes on or off?

If you do have an internal coil, a leaking coil could be introducing street pressure water into your boiler.

Unless the boiler and all the radiation are at the same elevation, 5 psi is too low.

Thanks Steve.

No, the hot water heater is now separate. Went with the GeoThermal which I LOVE!

For a failed bladder tank, doesn't the unit have to be water logged? That was why it was replaced in the first place.

One circulator was recently replaced, maybe I should do the other one? The pressure goes up when the circulator comes on and goes down when it goes off. The newer circulator is for the other half of the house - office space/guest area, so the temp is around 50 degrees ~ it doesn't come on much.

What is and how would I know if I have an internal coil? My boiler is fed by well water. Just replaced that dang pump this summer! I did have the plumber turn up the well pressure tank to 60 lbs. as I like good water pressure. Could that higher pressure have anything to do with the inlet valve on the boiler?

The house is two zone, two level and I agree that when it does drop down to 5 psi, it's frustrating.

Thank you for all your guidance.

AllieEm

Mike said:

Everything is pointing towards the xpansion tank. A new tank was installed, back in the fall. Why? Is the new tank the same size? If you turn off the burner for a hour or two, does the system pressure rise? I'm thinking the water feed valve is leaking by, and or the pressure gauge is out of calibration at low pressure.

Hi Mike,

The new tank was installed because the previous one was very old and water logged. The new one is the same size. When I turned off the boiler the other day to let the temp drop to change the automatic air bleeder valve, the pressure came down normally. The funny thing was that the boiler held steady at 12 psi for a few hours, even during the re-heating period, before the fluctuation started again. I did check the expansion tank when I had it off and it was at 10 psi. I added enough to get it back up to 12 psi.

Thanks for your questions and thoughts!

AllieEm

delta T said:

Check the connection to the expansion tank, there is a chance that the connection is clogged with rust and gunk and not allowing the x tank to 'see' the system. Does it connect to the bottom of an air scoop?

Other things to check:
1. Make sure the charge is correct on the expansion tank (should be checked when the tank is not connected to the system, should be = to your static cold fill pressure, usually 12-15 psi)
2. What kind of pump do you have and where is it in the system? (pics will help with this)

Hi Delta,

Yes, it does connect to the bottom of an air scoop. I did post photos of the system above. There is a photo of two other air scoop looking devices which I am afraid my education has not gotten that advance to know what they are and if they might be playing a piece on the chess board.

Thanks for your reply!

STEVEusaPA

The other two components are flow checks, to prevent flow from going into a zone if that zones circulator isn't running.
There's a lot wrong with the piping, most notably it looks like the expansion tank is isolated to one zone, which could cause the fluctuation.
The pumping towards the expansion tank, piped-wrong air scoop with the hy-vent, something is definitely mods here.
Also your boiler used to have an internal coil, but it's been abandoned, so it's not an issue/factor.
I also wonder if that gate valve is opened/working/not plugged with gunk. If you have to drain the system, I would replace that valve with an expansion tank valve.

bandit281

Have you replaced the prv.

rick in Alaska

Leave the fill valve turned off and drain the boiler pressure off. Does about two gallons of pressurized water come out before it drops to zero, or does it drop quick? If it drains quick, it could be the gate valve below the tank is plugged, or possibly the bladder in the expansion tank is stuck to the side of the tank.
Rick

AllieEm

Playing around with things again today, I noticed that the shut off valve to the expansion tank really doesn't move much from close to open. Only about a third of a turn. I think that will be the next thing to replace as everything/everyone's opinion really does point to the expansion tank. That is probably gunked up and stuck so not operating as it should. Probably closes well since I can take off the expansion take, but probably doesn't open as well as it should.

Will keep everyone posted, but may have to wait until warmer weather in order to drain everything. Headed for some more cold weather here in New England. As long as the pressure release valve is working, I don't mind dumping a few buckets of water per week while waiting the 41 days until spring.

I will say that this site is AWESOME!!! Thank you!!!

AllieEm

bandit281 said:

Have you replaced the prv.

Bandit what is the prv? Still a boiler newbie! Thanks!

AllieEm

AllieEm said:

bandit281 said:

Have you replaced the prv.

Bandit what is the prv? Still a boiler newbie! Thanks!

Wait!!! I got it! The pressure relief valve. LOL. No I haven't, but it does appear to be working good.

neilc

AllieEm said:

Playing around with things again today, I noticed that the shut off valve to the expansion tank really doesn't move much from close to open. Only about a third of a turn. I think that will be the next thing to replace as everything/everyone's opinion really does point to the expansion tank. That is probably gunked up and stuck so not operating as it should. Probably closes well since I can take off the expansion take, but probably doesn't open as well as it should.

I think you might of found your problem with that valve at the X tank.
That stem should turn several full turn.
the 2/3s your getting is just slack.
Try giving it a little extra umph counter clockwise(loosen),
that valve will probably jump open. and you can try tapping on the valve body gently at the opposite side from the handle at the same time as your twisting.
If the valve doesn't open, try closing it just a bit, 1 full turn, we're just trying to see if you're open or closed right now. Let us know where that goes.
If it opens you're good to go for now,
If it's stuck shut, well, either a pro may give it a shot, or as you said, replace it, but you want that tank back in the system.

nicholas bonham-carter

Loosen the packing nut a quarter turn, and that will often break the bond holding the stem from turning.
when you have completed this manoeuvre, tighten the nut up again to prevent a packing leak.--NBC

AllieEm

Thanks everyone. Will wait until tomorrow to attempt loosening it as it's easier to find a parts store during daylight hours than in the evening if it decides to leak. Will report back.

JUGHNE

PRV, could be the pressure reducing valve for water pressure regulation fill.........or PRV meaning pressure relief valve that open and dumps at 30 PSI.
Perhaps the relief valve could be called the "pop off valve" to clarify things.

There are times that the pressure reducing valve cannot deal with high pressure applied to it.....you had your pump jacked up to 60 PSI. So that has to hold 60 on one side and 12 on the other. IF old and tired it might be squeaking some water thru but eventually your pop off would open at 30 PSI.

Yes, that old gate valve above the tank could have up to a dozen rotations to open or close. Or eventually the guts come apart inside and could be stuck open or closed.
If you think you get it shut, you should be able to loosen the tank (when cold) without a lot of water coming out.

HomerJSmith

Well, the air charge on the X-tank has to be at the same pressure as the system pressure that is set by the boiler water feed pressure regulating valve. Are you sure that the air charge was even 12 psi when you installed the tank? If that air charge is low the water acceptance of the tank will drop to a point where it is totally filled with water forcing water out of the PRV. Shake the tank and see if it feels heavy and sluggish. Depress the schrader valve on the bottom of the tank quickly and see if any water comes out of it.

The reason that the pressure gauge moves higher when the pump turns on is that the gauge is registering dynamic pressure that the pump is creating.

Replace that red handled valve above the X-tank with the following valve: Webstone Valves Mfr Part#: 40612
https://www.pexuniverse.com/webstone-pro-pal-40612-ball-valve-w-drain

AllieEm

HomerJSmith said:

Well, the air charge on the X-tank has to be at the same pressure as the system pressure that is set by the boiler water feed pressure regulating valve. Are you sure that the air charge was even 12 psi when you installed the tank? If that air charge is low the water acceptance of the tank will drop to a point where it is totally filled with water forcing water out of the PRV. Shake the tank and see if it feels heavy and sluggish. Depress the schrader valve on the bottom of the tank quickly and see if any water comes out of it.

The reason that the pressure gauge moves higher when the pump turns on is that the gauge is registering dynamic pressure that the pump is creating.

Replace that red handled valve above the X-tank with the following valve: Webstone Valves Mfr Part#: 40612
https://www.pexuniverse.com/webstone-pro-pal-40612-ball-valve-w-drain

Thanks Homer, I think that will be the quickest fix and love your part recommendation. Actually going to wait until the weekend to replace it as temps are supposed to be in the high 40's. Makes it easier when shutting down the boiler than this dang 18 degrees.

newagedawn

the expansion tank and valve are bad!!!!!, simple as that

AllieEm

It was the valve above the expansion tank!!! It only turned like half a turn and now it's free. Turns many times now between the open and closed position. Will be putting in the new valve which Hormer recommended above this spring and probably a new circulator replacement as it's probably time for that too. Thank you to everyone with your thoughts and ideas. Sometimes we overlook the things starring us in the face.