Question About Purging Heating System

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Lawnguyland

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Just gone done with a bunch of work on my heating system so I had to purge the system after everything. My system has 2 zones, but they both tie back into the same return, so there's only one return valve. I shut the one return off, opened both zone valves at the same time, opened the bleeder valve with a long hose connected to it going outside the house into a bucket, then opened the pressure reducing valve all the way. Took awhile until I saw no air/bubbles coming out, but eventually I got there many buckets later and then I normalized everything. My question is, is it ok to do both zones at the same time if they loop back into the same return? From what I've seen, for the people who purge one zone at a time, each zone is on its own loop with its own bleeder and its own return valve. I figured it would be ok since they connect on the return, but wasn't 100% sure. Thanks.
 

jadnashua

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Shouldn't matter. Note that the water you put back in is likely to have some dissolved gases in it, but depending on what you have for air extraction, you may or may not need to purge air again.

Sometimes, it's hard to ensure flow through both zones, so it may work better to do it one at a time, especially if one zone is on a different floor as any flow will tend to take the path of least resistance, and may not reach the upper story (if it exists in your layout).
 

Lawnguyland

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Shouldn't matter. Note that the water you put back in is likely to have some dissolved gases in it, but depending on what you have for air extraction, you may or may not need to purge air again.

Sometimes, it's hard to ensure flow through both zones, so it may work better to do it one at a time, especially if one zone is on a different floor as any flow will tend to take the path of least resistance, and may not reach the upper story (if it exists in your layout).

One does go to the second story, so maybe it's better I just do it again, doing each zone separately. Beginner question: if I'm introducing new dissolved gases into the system every time I purge it... How do those gases get extracted? Is there something else that is extracting air and other gases from the system all the time? Should I worry about this? The house is 50 years old and the heating hasn't changed much.
 

jadnashua

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The volume of gas dissolved in the water isn't much, and if you have any sort of air extraction in the piping, it should remove it over time.

Note, some of those gasses will be oxygen, and that will cause rust on ferrous materials until it is all used up. That's why even a small, but continuous leak can be problematic...it keeps adding oxygen and causes things to continue to rust. Once all of it is used up, the water is pretty inert.
 
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