Air in Boiler System


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Old 11-12-14, 04:00 AM
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Air in Boiler System

40+ year old oil fired boiler with 4 zones, 2 pumps, and an outdoor wood boiler.

I currently have air in the system and had recently reconfigured my upstairs zone (basically drained the whole zone and moved some pipes around). I can't seem to get the coolant to go upstairs and back around. I did not put any air bleeders on the zone as I have a boiler drain in the basement. After pumping HVAC antifreeze into the system, it doesn't appear to be drawing in the outside water to make up for the difference. So I'm planning on shutting down the system this weekend and replacing some parts. I was planning on replacing the pressure reducing valve, backflow preventer and possibly the expansion tank. I just wanted to hear some thoughts on doing all of this work at one time. Will there be some risk with ruining these parts by pumping in the antifreeze back into the system using a 1/2hp motor/pump? Also I bought a Watts 1/2" 9D-M3 backflow preventer. Is this the right part for my application? (The guys at the local wholesale house never want to hand out advice especially if you don't have an account with them). Thanks in advance.
 
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Old 11-12-14, 04:37 AM
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Sounds like your on the right path.
Hope you bought propylene glycol, not ethelyene glycol.
You should not have created any problems by pumping in the glycol, but typically we would add a ball valve and a hose bibb to each side of the ball valve (in supply or return line of boiler), this way you can power purge the system and direct the drained fluid into a bucket to push back into the system. This way you get as much air from the system as possible.
You want to be careful about using auto fill valves with systems that have glycol in them. If the system demands fresh fluid, it will draw straight water and this will dilute your freeze strength.
Propylene glycol also does not like to be too watered down, improper mixtures can results in bateria growth in the fluid and sludge being formed.
 
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Old 11-12-14, 05:26 AM
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I'm not sure of the type of coolant? I know its not ethelyene glycol which is automotive antifreeze. I bought 5 gallons at the local HVAC store. I did not dilute it as I knew some water would be added back in which lowers the protection. I like your idea of the ball valves and hose bib. Right now I just have a hose bibb on the upstairs zone near the furnace before the zone valve.
 
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Old 11-12-14, 07:39 PM
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you do NOT want 100% glycol.
I would aim for 40 percent.

Part of the fill process is mixing the fluid down tot he 40 % concentration and then pumping it into the system.
Straight glycol will not mix well on it's own in the system.
Seen many snow melts fail because the prev. contractor failed to mix the glycol and water and ended up with area of straight or nearly straight water
 
 

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