Our trusty Weil-McClain CGX boiler works great, heating 3 zones reliably. One big problem: water slowly dribbles out the top of the air vent's shrader valve, even with water supply turned off and the valve cap tightened. The water spurts out vigorously when I depress the valve's pin. When I rap on the bladder pressure tank it sounds hollow at the bottom half, filled at top. When testing boiler relief valve, water dribbles out. Boiler pressure gauge reads 15 psi, temp minimum. (System off for summer.) The incoming water supply sequence is: 1. on/off valve, 2. backflow valve, 3. pressure reducer, 3. (another) on/off valve, 4. air vent, 5. boiler. Zone valves all are off. Circulator has not run for months.
Please ---------What's the problem? And what can I do myself to stop the dribble and right the system? Thanks!

 

The bladder-type expansion tank should have air on top and water in the bottom - not vice versa.

You said that when you check the relief valve, water dribbles out. Out of the relief valve discharge? When you lift the manual relief valve operator, it should flow faster than a dribble.

Water should not be coming out of the air eliminator if it's working properly. And, with a continual water leak, make-up water will be added at the same rate, causing harmful disolved oxygen to get into your system.

Photos might help us understand your system better.
Doug

 

Thanks for your interest, Doug. So far I've been able to maintain this boiler, but this leak has me baffled.
1. I'm probably reading it wrong, but the expansion tank sounds different top & bottom halves. There's what looks like a shrader valve on the bottom.
2. You're right, the water comes out of the relief valve like a regular faucet open a half turn.
3. Yep, the air trap is full of water, leaking from the valve cap. and will spurt forcefully if I depress the shrader valve pin. That's my main problem. For now the water supply is turned off. There are no leaks anywhere else in the system. For your reason, I'm reluctant to drain the system if I don't have to, but I do have to drain one zone to replace a radiator valve.
4. I'm posting three pics on my wife's Picasa photo site, with URL here. I'm not new to DIY, but I've never got involved with photos before. Hope it works. Thanks, Paul

 

Trying again with that photo link
Picasa Web Albums - Sandy - Boiler pictures
Hope this does it.

 

Making sure. The pics are at
Picasa Web Albums - Sandy - Boiler pictures
Thanks, Doug
Paul

 

Paul, something on my computer doesn't like Picasa... the page loads, but the pics don't... I'm sure it's on this computer, cuz it does it with anyones pics, not just yours... but from what I can read here, let's take it one thing at a time.

First, the AIR VENT... the thing that looks like this:



right?

If so, if that valve is leaking, and even with the cap screwed down tight? then it needs to be replaced.

Is that what yer talkin' about?

 

I just tried a different browser and I saw the pics...

You say it still leaks with the cap screwed down? weird... must have a crack around the stem or something...

You don't really have to drain the whole system... valve off as many of the zones as you can, close the incoming water feed, get the new part ready to screw it on... get some towels and/or disposable diapers ... drop the pressure in the system to zero.

Yer gonna get water, and get wet, but if you have a thumb ready to put over the pipe when you take the old one off, and the new one ready, you should be able to make the swap without draining, and won't lose too much water if you work quick.

 

I don't see where the expansion tank is located on your system but I really do not like where the make-up water is connected. The only thing connected to that boiler tapping should be the air vent. The make-up water can be connected almost anywhere else.

The air vent, if it is working correctly, will have water squirting out when the pin is pushed. You must leave the cap about one turn loose under normal conditions.

If your safety valve is more than five years old then replace it. It is cheap insurance vs. a non-functioning safety valve. If all you have on the boiler is the cold pressure of 10-15 psi then you won't get much flow through the safety valve when you manually open it.

 

I always put a valve under the air vent so you can change it easily. They make ones especially for that.

 

This is the 'special' valve that Bilbo is talking about... they often don't seal up 100% when you take the air vent off... you still have to drop the system pressure to 0, but it makes changing the vent LOTS AND LOTS easier!

KingSolar.com: No. 9AS Shortstop Automatic Shutoff Valve - for use with Maid-o-Mist No. 66, 67, and 78 Auto-Vents

When you go to change that out, make sure you get the right thread size and sex ! there's M and F threads, in both 1/8" and 1/4" ... the valve above is for the 1/8" threads.

 

Hey, thanks to all of you. I think I now am on top of this. I got another, but double-ended schrader valve cap and tightened the valve insert. That didn’t help, but applying the new cap did mostly stop the leak. But from what you’ve said, I’ll still replace the air vent so I can leave the cap loose, as prescribed. The shut-off valve & info is great, thanks. I’ll use that & even settle for a manual one if the supply counter doesn’t have the automatic one. And – good idea – I’ll replace the safety/relief valve while I’m at it. The system is 13 years old. So far I’ve replaced one circulator, one solenoid and several zone valves.

Remaining question: To drop the pressure to zero, first I can shut off both sides of all zones and the water supply. What then? Do I hold open the relief valve until the pressure gauge hits bottom? I could do that or partly drain the boiler from the lowest tap. The latter, with a hose connection, would be easier.

Again, thanks all. DIY is the greatest!

 

Opening the boiler drain valve would be the way to go.
Doug

 

Thanks Trooper. I have looked at those but actually I use a little ball valve with male on the bottom and female on top.

1/4" MALE NPT X FEMALE NPT BRASS BALL VALVE, 600WOG/150WSP, -40 TO 300 DEG F - Gauge Accessories - Accessories - Valves and Instruments