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lund0529 11-24-2007 12:17 AM

Air in Heil-Mclain CG Series 11

Doing a kitchen remodel, I moved a radiator line going to my second story. To do this, I had to drain my system, or at least part of it. There are three loops in the system, two to the second story, one to the first. I'm having some trouble getting the system refilled.

There are no bleeder valves in, on, or around any of the baseboard radiators (copper pipe with fins).

I have what I think is an air scoop on the top of the furnace itself, and a small bleeder valve on top of that. There is a line in from the water system which passes through a anti-backflow unit of some sort. The line from there can either be shut off, or directed to the furnace, or the horizonal expansion tank in the rafters. The valve to the expansion tank was closed when I started.

The flow into the furnace appears to be three separate circuits, each with a drain on top of a shut-off valve. These come down into the circulating pump, which goes into the furnace and also has a drain under it. Outgoing appears to be a large common pipe that separates to two and later a third. (Sounds backwards to me but there is a directional arrow on the scoop)

If I open the water inlet from the house water, it blows out the 30 PSI pressure relief valve on the furnace. The pressure gauge on the side of the furnace started out reading ~12 PSI. After draining, it still read 12 PSI. It read 12 PSI when the overflow valve let loose as well. So I think I have a bad gauge.

The first floor circuit seems to be kicking out heat. How to I get the second floor purged, filled and kicking out heat? (It's November in MN - brr...)

Thanks much,

ThomF 11-24-2007 08:15 AM

Purging Hydronic System
There should be provisions for vents at one of the elbows at each of your baseboards. I would be surprised if you don't have vents at these elbows, because the original installer must have had to purge the system. Usually they use the high point of the system to bleed out the air.

If you don't have any vents, you could add them fairly easily (take some pressure off the system first and make sure the inlet water valve is closed).

I have never done the following, but you could try it:
  • You could isolate each of your three circuits, one-by-one, to force the air pockets to the air eliminator on the boiler. Right now, with a single pump, the line with the air pocket has added resistance to flow and all of the flow is going through the other circuits. If you isolate the circuit with air in it, the air bubble should be forced to move around the system and if you have an air eliminator of some sort it should eventually take out the air.
I am surprised that your relief valve is opening when it sees pressure from your water system. This shouldn't be happening. Are you served by a municipal system, or your own well? If it's the later, perhaps your potable water system isn't set up correctly.

Let me know if any of this is helpful. (The reason I looked at your note is that I've been chasing around an air bubble in my 80 year home which is keeping my daughter's bedroom fairly cold. I can't easily isolate circuits in my system.)

Good luck,


ThomF 11-24-2007 08:51 AM

Purging Hydronic System

Originally Posted by lund0529 (Post 75818)
If I open the water inlet from the house water, it blows out the 30 PSI pressure relief valve on the furnace. The pressure gauge on the side of the furnace started out reading ~12 PSI. After draining, it still read 12 PSI. It read 12 PSI when the overflow valve let loose as well. So I think I have a bad gauge.


In thinking this over for another minute, I think you need to get your make up water supply functional first. You can't eliminate the air in your circuits unless you can replace the air with water. And you won't be able to replace it with water if your inlet water valve is shut off.


ThomF 11-24-2007 09:15 AM


In taking a quick Google search about purging hydronic systems, I discovered that more modern systems often have an air eliminator at the boiler, as well as purging valves. If you don't have air vents at your baseboards, then you must have a purging valve system at the boiler.

The purging valves get configured such that the water velocity forces the air pockets through the system until they come out at the boiler drain.

But again, you need to be able to open the water make-up valve.

I hope some of this helps,


lund0529 11-24-2007 10:04 AM

Thanks for the reply. I actually got it figured this morning. There are no baseboard bleeder valves, and the one on the "air purge" (air scoop?) is tiny, like a hole the size of the head of a pin.

Here is what I did. Hopefully it helps your bubble.

I needed to close off all of my circuits, the expansion tank, and the water influx. I closed the flow valve on each circuit, and opened the drain valve on one of the circuits. Then I attached a garden hose running to a barrel of the coolant water that I collected to the circuit drain. Then I attached a second hose to the bottom drainage valve and the other end to a sump pump submerged in the same barrel of coolant.

Now each circuit is basically a copper hose with air bubbles in it.

With the valve closed below the drain on the circuit, and pumping coolant in below the pump, I basically just flushed the circuit. Took about a minute. I closed that circuit's drain valve and repeated with the other two. All the coolant in the lines (and air bubbles) ended up back in my barrel of coolant.

Once the flow equalized, all I had to do was close the valves. The pipes are still a bit noisy from the air that was dissolved in the coolant, but I think that will pass with the air scoop in the days or weeks to come.

Now that I have the process worked out, I can drain and switch over to the clean new coolant.

Good luck - hope this helps!


ThomF 11-24-2007 10:32 AM

Great to hear that you are up and running! Unfortunately my system won't permit the innovative solution that you used -- good thinking. It appears that most modern systems are set up to essentially use the type of technique you employed, although most use the make-up water line to force the water (and entrapped air) through the circuits.

My system was originally a gravity system (no pump) and has large headers running through the basement. The old radiators were removed and copper lines from the headers were installed to feed new baseboard heat exchangers. As a result I don't have separate zones.

I also don't have an air extractor at the boiler -- just a small float valve for any bubbles that might occur in the boiler itself.

I do have vent fittings at each baseboard radiator, and a large faucet at the top of my system that I can use to purge large bubbles. So whenever I have to drain the system (like I had to do this summer to relocate a line), I usually have to go through a lengthy process to get rid of bubbles in the system. But once done, I don't need to touch it again for years.


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