Slow Pressure Loss


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Old 01-15-09, 04:32 PM
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Slow Pressure Loss

I'm running an old (33 years) American Standard boiler with tankless coil (w/storage tank on its own zone). I normally keep the supply valve shut and I've noticed over the past several months that the system gradually loses pressure until gurgling noises are heard in the 2nd floor zone (2 story house w/basement). Once I open the supply valve, a little flow is heard and pressure returns to about 12 psi (not sure how accurate boiler gage is). It then takes about a month or so before the pressure drops to near 0 and the 2nd floor gurgling starts again. I realize I could leave the supply valve open to keep this from happening but it would simply cover up this apparent slow leak. I've looked at all of the exposed pipe in the basement and don't see any sign of leaking and I see no evidence of the pressure relief valve spewing anything. The expansion tank (see photo links) is a bladder type, on the supply side and the label says it is charged to 12 psi. I knocked on the tank and it seems little water is in there (maybe the top 20%). Any ideas? Oh and what is that green thing next to the tank?

http://i169.photobucket.com/albums/u...k/DSCN1569.jpg
http://i169.photobucket.com/albums/u...k/DSCN1570.jpg
 
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Old 01-15-09, 05:29 PM
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The green thing is a flo-control valve - actually, a lift-check valve. It stops gravity flow, but allows flow when the circulator is running.

It's green so is probably a Taco. B&Gs are red.

You say that the pressure, after charging water into the system, is 12psi. Is that hot or cold?

For your pressure to decrease over a month suggests a leak in the system. Is the relief valve simmering, by chance?
Doug
 
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Old 01-15-09, 06:13 PM
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Wise-a55 answer (and normal explanation)

Oh and what is that green thing next to the tank?
Ummmm... a "TACO 220 UNIVERSAL FLOW CHECK" ?

It's a check valve. Water only flows one way when the screw on top is screwed all the way IN... it looks like it's OUT somewhat. You will have 'gravity flow' in the system when the screw is out... the hot water floats out of the boiler into the heating zones when it's out (open).

It looks like the auto vent on top of the air scoop was leaking at one time (water drips down the tank)... has that been ruled out as a source of leakage?
 
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Old 01-16-09, 09:03 AM
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That was 12 psi hot boiler although the fresh water supply line is not heated. I'll take a closer look at the autovent valve. I'll put the mechanic's stethoscope on the relief valve and listen. Thanks guys.
 
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Old 01-16-09, 07:05 PM
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Give that man a cigar! I got up there and took a closer look at the autovent and there was a little pool of water sitting on the top surface.... So I wiped it off and got a look at the make/model (with a mechanic's mirror) and I find it's a Taco 1509SI or maybe 1509SL or ? I've tried several possible combinations and can't pull up anything for it on google. The only other markings indicate it was made in Italy and (maybe) a date of 05/99. On the Taco site, it looks like the Hy-Vent model in their catalog. Have I gotten the number wrong?
 
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Old 01-16-09, 07:56 PM
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Any of the autovents will work... Maid-o-mist #67 probably ... but one quickie way to check if that's the sole source of leakage is to screw the cap down tight for a while and see if the pressure droppage stoppage... there's probably little or no air in the system to vent at this point anyway, so it could wait till spring to replace.
 
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Old 01-17-09, 08:20 PM
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Thanks NJ. As long as it stays a slow leak it can wait till summer... I was hoping to match the model number for knowing what the threads are. It's such a short threaded section exposed that I can't tell what they are. What is the most common do you think?
 
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Old 01-18-09, 08:38 AM
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Most likely 1/8" NPT (Male), but some are 1/4" NPT... there are Female varieties also.
 
 

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