Expansion tank question

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Old 10-08-09, 08:27 AM
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Expansion tank question

I'm not sure if I am having separate issues, or if it's all related so let me give a little of the background story. Gas boiler with water dripping from the backflow preventer valve on the water feed line. This was happening over the summer with the boiler off and the pressure valve reading 0. Maybe 1/2 gallon every 2 weeks. I decided to replace the existing reducing valve with a dual feed unit, and I also replaced the existing backflow preventer with a new 9D unit. I turned on the boiler and it quickly went up to about 32 psi on the pressure gauge, and water started dripping from the relief valve. I pressed the schrader valve on top of the expansion tank and some air came out (little water mist too) and the pressure went right down to 20. Let the boiler run for about an hour more and it stayed right at 20 and there was no more dripping. The other complication here is that the house is in NJ and I live in Long Island, so I only make it out there every few weeks. Is the tank in need of replacement?
 

Last edited by deuce5; 10-08-09 at 08:36 AM. Reason: forgot to say something
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Old 10-08-09, 04:12 PM
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It does sound as though there may be 'multiples' here...

After you installed the new reducing valve and backflow preventer, and turned on the water, did the pressure rise up and STAY at 12-15 PSI ?

And then only rapidly shoot up to 32 AFTER you fired the boiler?

If so, I would say that your expansion tank needs service... if it's a conventional steel tank, it should be isolated, drained completely and returned to service... if it's a bladder tank, you would need to check that the air charge on the air side of the tank was between 12-15 PSI with ZERO pressure on the water side.

I believe that when you let the excess pressure off by bleeding, that you only masked the problem temporarily... here's why: Now, when the boiler cools, the pressure will drop below 12 PSI because you let pressure out when the boiler was HOT... when it cools again, the water will contract, and the pressure will fall... the new reducing valve will feed water back into the system, and the next time it fires up, the pressure will skyrocket again, and the relief valve will open again... and let water out again... and the boiler will cool again, and the valve will let water in again... ad nauseum, etc, etc, forever and ever, amen.

So, check the expansion tank.
 
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Old 10-08-09, 04:48 PM
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I understood him to mention a schraeder valve, which must mean a bladder-type expansion tank. When he pressed the pin of the schraeder valve, air and a mist of water came out.

I'm suspicious of the expansion tank.
 
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Old 10-08-09, 05:14 PM
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I pressed the schrader valve on top of the expansion tank and some air came out
Good catch Mike! I read too fast, and didn't notice the expansion tank part... ASSumed he was talking about the auto air vent...

Yeah, deuce, that was a boo-boo... you should NEVER let the air out of an expansion tank! and that 'mist of water' may also indicate that the bladder in the tank is compromised and leaking through...

Is the tank installed with the schrader pointing UP, or DOWN?
 
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Old 10-08-09, 08:42 PM
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After you installed the new reducing valve and backflow preventer, and turned on the water, did the pressure rise up and STAY at 12-15 PSI ?

And then only rapidly shoot up to 32 AFTER you fired the boiler?
That is correct, exactly what you said.

I now see why it was bad to press the schrader valve. I guess I just wanted to see if any water was going to come out. I really think I didn't let that much out. I held it maybe 1-2 seconds. The schrader is pointing UP. Next time I go I will check the pressure on the tank.

So would it be best to just replace the tank or could it be something else? We don't live at this house, it's a house we are in the process of selling and nobody currently lives there. The buyers of the house are probably going to be having a home inspection done soon. I don't want there to be water dripping while that is going on!
 
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Old 10-08-09, 09:06 PM
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Being that the tank is installed with the schrader UP, you might be able to 'get away with' just recharging the existing tank, but that would be somewhat unscrupulous...

1 to 2 seconds is probably long enough to let almost all the air out of that tank.

And the fact that you got water mist means that the bladder is probably shot...

How old you figure the tank is?

They aren't that expensive really, and I would say if you wanted to do the right thing, replace it.

Make sure you check the precharge on the tank before you install it. There should be 12-15 PSI to start...
 
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Old 10-09-09, 11:44 AM
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The tank is probably about 10 years old? I seem to remember a date on the boiler around 1999. I will probably just get a new tank. Thanks for the help.
 
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Old 11-06-09, 09:31 AM
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So I replaced the tank with a new one of the same size and model (Extrol No. 30) and I am still getting water dripping from the relief valve. The new tank had a 12psi charge in it when I installed. I bled the system and everything else seems to be working fine. I'm lost here. Could the expansion tank be of insufficient size or design? It's a 1700 sq ft. 1 story ranch house with 1 zone of hydronic baseboard heaters.
 
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Old 11-06-09, 03:34 PM
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Let's forget the dripping relief valve for a moment...

The real question now is : After you replaced the tank, is the pressure under control? Is it like 12-15 when cold, and maybe say 20 PSI HOT?

If the relief valve is dripping when you have less than 27 PSI in the system, and you are sure the pressure gauge is reasonably accurate, then the relief valve should be replaced.

I and others advocate changing them every 5 years... leaking or not.
 
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Old 11-06-09, 05:07 PM
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I will check tomorrow. When I replaced the tank, while cold the pressure gauge on the boiler said 15. Then I ran the heat for a few hours and it never went beyond 20. There was no dripping at that time. I have not been out at the house since then (2 weeks), but the real estate agent reported water dripping out of the overflow a week ago. It is a brand new relief valve as well. I will have more info for you when I go tomorrow. Thanks.
 
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Old 11-09-09, 02:02 PM
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I ran the boiler for a few hours and it never went higher than 21 psi. The water that is discharging is much less than it was before I changed the expansion tank. It was basically just a small puddle maybe 3 inches in diameter. This is also with a 1 month old relief valve. I was just under the impression that is should NOT discharge at all.
 
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Old 11-09-09, 03:34 PM
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Originally Posted by deuce5 View Post
I ran the boiler for a few hours and it never went higher than 21 psi. The water that is discharging is much less than it was before I changed the expansion tank. It was basically just a small puddle maybe 3 inches in diameter. This is also with a 1 month old relief valve. I was just under the impression that is should NOT discharge at all.
You are correct about the pressure relief valve, it should not discharge unless the system is over-pressurized. Since it is new and the is dumping water, there are a few possibilities that come to mind.

One is that the pressure gauge is wrong and the system pressure is near the relief threshold.

Another is that the pump and/or zone valves and/or TRVs are causing the pressure to spike at the relief valve location. This can happen when the circ pump turns on and a zone valve isn't open or too many TRVs are closed off. The spikes the pressure and the relief valve opens.

It may also be that the expansion tank, circulator, and relief valve locations are all wrong. Which is causing a pressure spike when the pump is turned on.

Al.
 
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Old 11-09-09, 03:57 PM
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Or, there is a piece of 'crud' under the valve seat.

Try this:

Put a bucket under the discharge pipe, and pull the lever on the valve full blast for a second or two, and let go of the handle and let is SNAP shut, instead of just releasing it.

I never trust the pressure gauge............
 
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Old 11-10-09, 08:24 AM
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I'm not sure about the pressure gauges accuracy, but I do remember that when I had first changed the backflo valve and reducing valve the gauge read about 31-32 when it started dripping out of the relief valve. Then when I purged some air out of the expansion tank, it went down to 20 and stopped dripping. This is just difficult for me to deal with because I don't live there, and I only spend a few hours there every few weeks. During the time in between I have no idea what is going on there.

Like I said it's definitely dripping A LOT less than it originally was. I just wish it would stop all together. I will try opening it and snapping shut next time I go.

Here are some pics of what I have going on:




Here is a pic of the system before I did any work on it:

 
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Old 11-10-09, 10:42 AM
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Is there an expansion tank for the water heater? Unless this system is on a well there needs to be one. IOW, if on city water need an expansion tank for the water heater.

For the boiler, isn't the pressure relief valve near the expansion tank? In the upper left of the first picture, off the front left corner of the boiler.

Al.
 
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Old 11-10-09, 04:48 PM
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You really only need the expansion tank on the water heater if there is any type of CHECK VALVE on the cold side feeding the heater. If the city water comes straight into the home without a pressure regulator or check valve, no tank is needed, as the city system will absorb the pressure increase. SOME city water system pressures are very high, and these homes will have a regulator to drop the pressure, and there is a check valve in those regulators.

Yes, I see the proper relief valve on the boiler also. I'm not sure why the other one was added? That second one next to the regulator is not an ASME approved model. You don't need it if the one on the boiler is good to go... I would just take it out and replace it with a piece of straight pipe and be done. The one on the boiler isn't leaking, right?
 
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Old 11-10-09, 05:55 PM
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I may be wrong but I thought city water feeds are required to have back feed prevention. Built into the water meter?

Where I was going is that excess pressure on the feed regulator valve may be causing the boiler to over pressurize.

Al.
 
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Old 11-10-09, 06:15 PM
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Maybe newer meters, newer codes, etc... I don't think older meters have backflow prevention... could be wrong, I'm no plumber! But, even a system with private well would need one if there were a check valve in the cold line (which is recommended on a private well system because the swings in pressure in such a system will cause the water heater to 'breathe' in and out of the cold supply) but this is just a _little_ off topic!
 
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Old 11-10-09, 06:18 PM
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Originally Posted by OldBoiler View Post
I may be wrong but I thought city water feeds are required to have back feed prevention. Built into the water meter?
No - not at least where I live or have lived.
 
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Old 11-10-09, 07:27 PM
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Yes, I see the proper relief valve on the boiler also. I'm not sure why the other one was added? That second one next to the regulator is not an ASME approved model. You don't need it if the one on the boiler is good to go... I would just take it out and replace it with a piece of straight pipe and be done. The one on the boiler isn't leaking, right?
I put it there, but I'm not sure why. I guess when I went to go buy a new reducing valve at HD it was the dual unit so I just put that in. But now that it's there, it shouldn't drip anyway right? I have one of those on my boiler at my house in NY and it doesn't drip. And no, the other relief valve on the boiler does not drip at all.
 
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Old 11-10-09, 07:41 PM
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That's right, it shouldn't drip anyway... so try the snapping shut idea and see what happens. If you shut the valve between the boiler and the relief valve you can use the water supply to flush through instead of letting it out of the boiler...

You could also plug it, but if a home inspector see that, he might go bananas, and you wouldn't be able to explain it to him...

Hopefully the 'snap' will do it.
 
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Old 11-10-09, 08:03 PM
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You could also plug it, but if a home inspector see that, he might go bananas,
LOL, yes I would think so! And as I'm sure you know, in NJ they LOVE to inspect everything. I'll let you know how it turns out. Thanks.
 
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Old 12-01-09, 08:33 AM
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Just an update on this: I had not been out at the house for about 2 weeks and now I go and the bucket is dry. The heat was on and it has totally stopped dripping. Gotta love problems that fix themselves. Thanks again for all the help and advice.
 
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Old 12-01-09, 03:30 PM
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Thanks for the update!

Did you happen to notice the pressure? Everything seems good to go now I guess...
 
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