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.