Expansion tank that wont take water?

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  #1  
Old 02-13-13, 12:26 PM
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Expansion tank that wont take water?

I understand how expansion tanks work, but this one has be stumped. The boiler behaves like the tank is water logged, but it's not. It's at 12 psi cold and opens the pressure relief at 30 psi around 185 degrees. The expansion tank reads 12 psi no matter what the boiler pressure is and is cold from top to bottom. It also feels empty even when the relief valve opens. The tank is only two years old and I can't understand how it could fail this way. There are no valves connected to it. It sits on the bottom of a spiral vent. Can those get clogged?
Any advice appreciated!
 
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Old 02-13-13, 01:15 PM
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No water out the air valve, right?

What happens when you let all the air out of the tank?

Let's just say that 'somehow' (and I can't imagine how) the bladder is 'stuck' to the underside of the tank lining. Maybe letting the air out would un-stick it...

Or at least give some additional diagnostic data...
 
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Old 02-13-13, 03:07 PM
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Right, no water out the air valve. It doesn't seem to matter what I pressurize the exp tank to. Even with no pressure, it's still cold on top. The bottom of the spirovent is hot, but the tank surface right under it is not. This is with the boiler at ~20 psi. It acts like it's not really attached to the system. The only things it seem to me that it can be is the spirovent is plugged somehow or the tank is. Neither makes sense to me.

The one thing I didn't try is raising the tank pressure higher than the boiler pressure and see if it affects it at all. Maybe it will loosen something up.
 
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Old 02-13-13, 03:13 PM
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The one thing I didn't try is raising the tank pressure higher than the boiler pressure and see if it affects it at all. Maybe it will loosen something up.
I don't think that will help, it probably will only push the bladder up harder...

Try letting all the air out while the pressure is still on the system side. That should allow the water to flush into the tank. If that don't work, yer gonna have to pull the tank.

Before you reinstall it, add a couple extra valves:

 
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Old 02-13-13, 03:33 PM
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OK, I let all the air out and it didn't affect it at all. The top of the expansion tank is still cold. Then I pressurized it to 25 psi, also no effect on the boiler pressure which was about 15 at the time. Guess I'm taking it apart tomorrow. Something weird is going on.

Good idea on the valve and drain. Much easier than flushing the whole system when you have to open it.
 
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Old 02-13-13, 04:38 PM
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Very bizarre!

Please be sure to let us know the outcome because this needs to go 'in the book'!
 
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Old 02-13-13, 04:50 PM
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The tank does not get hot/cold pe se'. Upper ? Lower? At least mine does not that is noticeable...

Probably you are chasing demons?

Possibly you have a fill valve issue.....
 

Last edited by lawrosa; 02-13-13 at 07:34 PM.
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Old 02-13-13, 05:03 PM
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Probably you are chasing demons?
It's at 12 psi cold and opens the pressure relief at 30 psi around 185 degrees.
A very demonstrable demon if such be the case.

There is clearly a problem here!

expansion tank reads 12 psi no matter what the boiler pressure is
If the tank is properly charged to 12 PSI and the boiler pressure rises during heating, that pressure rise should be reflected at the air valve on the tank.

Jim, let me ask a couple more questions though, following Mike's line... just to be sure:

Does your boiler also make domestic hot water via a tankless coil?

Have you tried setting the cold pressure of the boiler at 12 PSI and CLOSING the MANUAL water feed valve to eliminate the fill valve as a possible culprit?

When you charge the tank with air, are you doing so with the BOILER AT ZERO PSI?

If not, then you don't really have a 12 PSI air charge in the tank.

Please read and follow the step by step instructions for PROPERLY charging the expansion tank to 12 PSI before going much further... Follow this procedure to the LETTER...

-----------------------------------------------------------------------------

1. Shut off boiler and allow to cool to under 100F.

2. Shut off water supply line to boiler.

3. Drain only enough water from the boiler drain (note: this does not have to be THE boiler drain. It can be ANY drain valve on the system. Use the one that is most likely to be able to not leak when closed again!) to drop the system pressure to ZERO. REPEAT: DO NOT COMPLETELY DRAIN THE BOILER! ONLY ENOUGH TO DROP THE PRESSURE TO ZERO!

4. With an ACCURATE tire pressure gauge, check the air charge in the tank on the air valve opposite the end of the tank that's connected to the system. If ANY water comes out of the air valve, the bladder inside the tank is shot and the tank needs replaced. If no water comes out the air valve, and the pressure is less than 12-15 PSI, continue to step 5. If the pressure is OK, turn the water supply to the boiler back on and re-pressurize the system, turn the power back on to the boiler, no service is necessary.

5. Using a bicycle pump, or a small air compressor, add air to the tank until you have 12 PSI air charge.

6. Check the boiler pressure gauge again, and if it has risen off ZERO, drain some more water from the boiler drain until it is again at ZERO.

7. Check the air charge on the tank again. If it is below 12 PSI, add air to the tank until it is at 12 PSI.

8. Repeat steps 6 and 7 until the boiler stays at ZERO and the tank stays at 12 PSI. At this point, the tank is properly recharged and the water supply can be turned on to re-pressurize the system, turn the power on to boiler and return to service.

----------------------------------------------------------------------------
 
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Old 02-13-13, 06:30 PM
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The auto fill is shut off, but it doesn't seem to make a difference. The 12 PSI in the tank is the same with no pressure (and a cold boiler) and with anything up to the 30 that opens the relief valve. The pressure is the same in the tank regardless of the water temp in the boiler. It does have a tankless HW coil. I swear it's as if the tank isn't connected.
 
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Old 02-13-13, 06:42 PM
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Jim, I know I'm asking the same thing over and again... I'm going to phrase it differently this time though...

You said that your tank is connected to your 'spiral' (do you mean SpiroVent here?) vent.

That implies to me that it is HANGING with the AIR vent pointing DOWN. Is that correct?

Would it be possible to take a picture of the tank and the SpiroVent and post it? Just so we know that someone isn't crazy?
 
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Old 02-13-13, 07:28 PM
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Here's a pic. I think I might be chasing demons too. But I don't know where. Just to recap:

Fill Valve is off

Boiler pressure at 160 is 12 PSI

Boiler pressure at 180 is 20 psi

Boiler pressure at 195 opens the relief valve at 30 psi (just a test, usually set for 180)

The expansion tank pressure seems to have no affect at all on the boiler pressure. I've tried 0 psi cold to 25 psi warm. No change in boiler pressure. The tank is always cold, even on the top an inch from the input.

No water comes out of the schraider valve. Even when drawn down to zero.

I understand how this is supposed to work. I replaced this tank two years ago when the diaphragm let go in the original one.

I realize this doesn't seem to make sense...
 
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Old 02-13-13, 07:34 PM
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What size tank is that? What was there? What type of heat emitters do you have?

It would seem the tank is too small.... ( But two years there?)
 
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Old 02-13-13, 08:27 PM
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It's the same size tank that's always been there (12 yrs). I replaced it two years ago but it's the same size. Even the same brand. The boiler is 112K BTU and heats 2500 sq with baseboards.
 
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Old 02-13-13, 08:30 PM
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Just for a 'sanity check', I HAVE heard on two occasions of the bladder/diaphragm 'sticking' to the inside of the tank. But both times this has been on a NEW TANK INSTALL and as I recall letting the air out managed to un-stick it and the tank worked properly from then on...

It sounds as though the same thing has happened here... it's the exact same symptoms... but WTH? the tank has been in service for two years!

Are you running antifreeze by any chance?

If it were my tank, I would be firing up the air compressor and an air fitting for the pipe connection so I could pressurize the bejeezus out of it not connected to the system...

Mike, you seem to be missing the fact that the pressure in the tank DOES NOT CHANGE. If he puts 12 PSI in the tank and runs the boiler up to 30, there is STILL 12 PSI in the tank... and that is IMPOSSIBLE. Boyle's law and the laws of physics say so... With 12 PSI of air in the tank, when the boiler goes to 30, you will read 30 on the air valve because the pressure transfers through... try it on yours if you don't believe it.
 
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Old 02-13-13, 08:43 PM
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NJ has it right. It's as if the tank is capped off. It's pressure is completely independent of the system pressure. It also feels empty and cold even with no pressure in it but 20 psi in the hot system. I'm pulling it off tomorrow to have a look. I'll let you know what I find. No anti-freeze or other additives.

Does the spirovent directly connect the tank with the input and output ports or is there something in between? It's like that bottom port that the tank is connected to is blocked. Is that possible?
 
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Old 02-14-13, 06:34 AM
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Bottom of SpiroVent is wide open to system.

In the bottom portion of the SV is a 'scrub brush'. Literally looks like a round wire brush. If there is a blockage there, it would have to be quite large...

The top part of the SV contains the 'float assembly' and it unscrews from the body but you should use a 'strap wrench' to avoid damaging the body. There is a large O-ring that seals the two halves, so it might be a good idea to have one on hand before taking it apart, if you decide it becomes necessary to do so. I don't think you will have to open it.

This is really a curious one!
 
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Old 02-14-13, 11:06 AM
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OK, so the answer is... The spirovent was indeed blocked. When I took the tank off I had a bucket ready for the water that would spill out of the vent, but none came out. The tank port and the inlet/outlet has a piece of tube or pipe between them (vertical, open end to tank and top vent). I stuck my finger up there and it seemed to be one solid piece (not perforated or a brush). As I started to try and move it around, dirty, rusty water started to dribble out. So I put the bucket under it and opened the feed water. A bunch more dirty water came out and then it started to run clear. Now when I stuck my finger up there I could move that tube around, maybe an 1/8" in all directions. I tried to open the vent, what a joke. Strap wrenches, even 24" pipe wrenches wouldn't budge it. I was afraid I would break the casting so I stopped.

The tank seemed fine. The diaphram was all the way to the top and went down when I let the pressure out. I changed it anyway since they are only $30 and I had it out.

So now everything seems happy. The pressure is stable at 15ish and the top of the tank is hot like I would expect. I wish I could have gotten that spirovent apart to see what was really in there, but it wasn't an option. It still works though as it was venting as I was refilling the system. Lots of fun, thanks for the help!
 
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Old 02-14-13, 02:15 PM
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Very strange that would get blocked up. I guess just rust and stuff from the black steel pipes?

Did ya put them extra valves between the SV and the ET?

I tried to open the vent, what a joke. Strap wrenches, even 24" pipe wrenches wouldn't budge it. I was afraid I would break the casting so I stopped.
Yeah, they can be tight! I bet that's one of the reasons that you can buy the whole top part as a 'replacement' part!
 
  #19  
Old 02-15-13, 07:29 AM
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Maybe as part of the maintenance put the valves/drains in like trooper showed. On the spirotherm website they make a combination air/dirt separator with ball valve to drain dirt out. Probably not cheap though. At least having valves/drains will make future service easier.

Maybe just an extra section of pipe on yours giving dirt somewhere to settle or section with T, with expansion tank off to side and straight section below spirovent with valve where dirt can settle and you can drain it with out dirt getting to expansion tank as easy.

Might be what caused old one to fail also. They also separate the spirotrap for dirt only. Spirotherm Dirt Seperators , Spirotrap Dirt Seperators , Spirotherm Seperators - PexSupply.com
 
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