When to bleed coin vents?

austin907

I recently had my system bled by a technician to remove air and that got the majority of it but whenever the second floor calls for heat, I still hear a little trickle sound while it is running. I was hoping to get rid of the air myself using the coin vents instead of calling out a technician again. My question is, what is the best time during the heating cycle to open the coin vent and at what point do you close the coin vent? Some background on my system: gas-fired cast-iron boiler with two zones on zone valves, copper fin tube. If any more information or pictures would be helpful, let me know.

JUGHNE

One theory is to run the system to get very hot, then shut down the power and let sit for maybe 1/2 hour. This may let any air migrate up to the high points.

Then open vents until solid stream of water flows...water will be hot!
Close up and restart boiler.

You need to have adequate pressure in the system to insure that water is up to the top of the system. 12-15 PSI cold and maybe 20 hot.

hot_rod

Is there an air purger near the boiler, that should get the last of the air if it is circulating 

Post a picture So we can see what you have

austin907

austin907

JUGHNE, I'll try that. I have been trying something similar where I just turn the second floor thermostat up for a while and then turn it low and let it sit for 15 min or so and then try opening the coin vents until I get water which is almost immediately.

austin907

hot_rod, there are some automatic air vents but no air separator. Was considering having one installed, especially if air problems persisted. The boiler (Weil McClain CGa-4 says it has an internal air scoop.

austin907

Tried to purge the remaining air from the coin vents until a solid stream of water flowed which was almost immediate. Unfortunately, now the sound has gotten even louder. I'm considering having a technician come out to purge the system again and install an air separator on the supply header (if there is room) or on the second floor zone only. Since I hear sloshing at the near boiler piping as well and the fin tube is hot that the air in the system is circulating and installing a air separator would remove it.

mattmia2

Is the little cap loose on those 2 automatic air vents? It needs to be loisevfor the to work. One is off the top left of the boiler, the other is on the bend just below the unit heater.

I question that unit heaters fan right next to the draft hood of the boiler.

Shane_2

If you have heat flowing to both baseboard zones, and to the unit heater, I would close the red handle ball valve under the can vent(unit heater) on the suction side of the pump.

Let it alone for a few days, and see if that helps. You may be sucking air into the system from that vent.

And check the pressure- cold and hot

austin907

@mattmia2 The caps on all three automatic air vents are loose. I checked that they are one full turn from fully closed which is fairly loose. The third air vent is on top of the unit heater. The unit heater is a top/bottom connection style. Regarding the unit heater fan, I have yet to run the unit heater since we moved into the house. Even on -10 F days, the garage stays around 50 F just from the piping and jacket losses from the system. When I tested the fan, it seems to blow far enough away from the boiler draft hood that it wouldn't cause any pressurization issues.

austin907

@Shane_2 I'll try that, thanks for the suggestion. There is a third automatic air vent above the unit heater.

Could the automatic air vent above the unit heater cause the same problem? If so, I'll just close the cap on that one since it doesn't have a ball valve. Regarding pressure, the supply outlet of the boiler reads around 15 psig. I don't want to let the system cool off at this time of year to check the cold pressure since we have been having record low temperatures.

Derheatmeister

Is the system circulating pump installed on the return side of the Boiler ? (Pushing into the Boiler)
Is the makeup/expansion tank installed just prior to the inlet side of the Circ ?
If so that can sometimes cause problems with air infiltration..(Sucking in air)
Are you operating the system with a Large setback ?
If this was my system i would probaby repipe it to a "Pumping Away" type of setup and add a couple Tees for a indirect fired waterheater when the time comes to replace it the current one.

austin907

@Derheatmeister Yep, the circulation pump is installed on the return side of the boiler. The expansion tank and make-up line are both installed directly prior to the pump. It is all pipe in accordance with the IOM (Weil McClain CGa-4). I do not have setbacks on either zone since it takes too long for the space to recover after the set back. The upstairs zone is set to 72 and the downstairs zone is set to 70. Yeah, i's not the ideal set up for pumps away since it is on the return but since the pump is "pumping away" from the expansion tank/fill line the system shouldn't have an issue with it. I do like the idea of the indirect fired water heater to increase the efficiency of it.. The current one is 17 years old so it's just a matter of time before it goes.

JUGHNE

It sounds like you have a pretty air tight garage. How big is it, 2 or 3 stalls?
With the boiler and water heater in that room, it needs to be a certain size for adequate combustion air.
And the fan coil unit might create a minor pressure reduction in the boiler corner,
perhaps inducing some down draft of the B-vent flue pipe.

It looks like you have the boiler install manual lying on top of it.
Early in the install instructions it has the requirements for combustion air based on total btu burning in the room and the cubic feet of air space required in that room.
It would be worth checking this out IMO.

Daveinscranton

Any chance that a copper (sweated) joint has come apart, or for whatever reason to picked now to leak?  If you have an auto fill, maybe not so obvious unless you see a puddle somewhere.  Might suck in a little air and drive you nuts trying to bleed things.

Just a thought.

austin907

@JUGHNE It is a slightly oversized two car garage. I tried to seal obvious gaps when I moved in (besides the combustion air inlet). I also installed some insulation on the inside of the garage door to reduce the heat loss through that. I read through the manual and it requires two air openings (one within 12" of ceiling and one within 12" of the floor) of 1 sq in / 4,000 BTU/HR if it is installed in a building of unusually tight construction. It also mentions that if the room is bigger than 50 ft2 / 1,000 BTU/HR then it would be fine. The garage is 600 ft2 and 10 ft tall with a 100,000 BTU/HR boiler input so I think I'm good. Not sure about the water heater though but am planning to have that replaced with an indirect one in the future which wouldn't require a vent.

austin907

@Daveinscranton The boiler was installed two months ago and I haven't seen any leaks since and have checked fairly regularly. The boiler also has a drip pan installed below it so I think it would be easier to notice if there was a leak.

Derheatmeister

If the boiler was installed just two months ago it is to bad that the piping arrangement was not as a Pumping away setup..
I understand that the exp.tank and the feed are prior to the circ but you must consider the head that must be overcome (Boiler and piping arangements)
If you have no obvious leaks anywhere i would take a look at the HX..
You could also do a combustion test which may reveal a possible leak.

Paul Pollets

It's hard to purge air when the pump is on the return pumping towards the expansion tank. There should be a ball valve and purge drain on each zone return to make it easy to purge at the boiler, without using the coin vents. If the piping is corrected and the pump moved, you'll only have to purge once.

austin907

@Derheatmeister I agree that it would be more ideal with the pump and fill line on the supply side, however the manufacturer IOM showed them on the return so that is what got installed. The system I had replaced was installed in the same way but never had any problems with air. The company that installed the boiler already sent out a technician twice to remove the air from the system but after a couple weeks the sloshing noise would slowly come back until it sounded like a waterfall every time the second floor zone calls for heat. I'm just trying to figure out if the system can be successfully purged in it's current configuration or if re-piping the system / installing an air separator is necessary.

austin907

@Paul Pollets While the pump is on the return line, the pump is not pumping towards the expansion tank but rather is pumping away. There are indeed combination ball/purge valves on each zone's supply and return which is what the technician was using to purge the system.

austin907

Trying to understand to pumping away concept a little better... I've read Dan's pumping away book myself and my understanding was that the main issue with pumping towards the expansion tank was that in systems with a high head pump, that the differential pressure the pump generates would be subtracted from the expansion tank pressure and could potentially cause cavitation at the pump inlet if the resulting pressure there was below the required NPSH of the pump. I agree that the piping schematic presented in Dan's book which shows everything on the supply side is a great basis of design that will result in minimal problems but I thought the main idea is that you pump away from the point of no pressure changes (expansion tank/fill line) which is done in this install. I would rather spend a little money on a air separator rather than spend a lot of money on re-piping all the near boiler piping. Let me know if I'm misunderstanding the pumping away concept though.