This should be very straight forward since the supplies and returns have individual ball valves and purge valves for shut off and draining. Close the ball valves for the zone you're going to work on. Attach a garden hose to the drain for that zone and open the drain. Once the pressure is relieved it'll pull a vacuum. At a convenient location for the baseboard you're going to remove start to cut the pipe. Once the cutting wheel has started to go through the pipe ( I assume it's copper) the vacuum will pull the water out of that loop and you'll be safe to take that section out.

After the work is done open the supply side ball valve (the one at the zone valve) and manually open the zone valve. the system pressure will push water through the loop and out the hose. When it sounds like most of the air is out close the purge valve, open the return side ball valve and close the zone valve.

Dapoppa,

Thanks for explaining this. It seems straightforward. I will attempt this soon and post back if I need further help.

One additional question - how can I add antifreeze to the boiler when refilling? There is currently a purple colored antifreeze in the boiler. A small quantity of this fluid drained out when I replaced a broken circulator on this boiler. There are ball valves on both sides of the circulator, so I could limit the amount of fluid that leaked out during the repair. When draining an entire zone soon, I expect larger quantity of fluid to drain out. So, I'd like to refill with antifreeze-water mix.

It can depend on what the concentration of A/F is at present. If it's at least 35% right now then just draining and refilling one zone shouldn't make much difference. Are you sure it's antifreeze? Is there a tag or sticker indicating when and how much was added? I ask because EK ships a quart of 8-Way boiler treatment with each system that's to be added to the system to clean and protect things. That'll usually have a purplish color.

If you find that there is A/F and the concentration is less than 30% when you're done then turn off the automatic feeder, close all the ball valves to the heat zones and drain about a gallon of water from the drain under the boiler. Remove the automatic air vent on top of the boiler. (That's the thing that says "Warning" that is visible in the picture.) Use a funnel to pour in a gallon of 90-95% concentration A/F and replace the vent.

Open the feed valve to repressurize the boiler. Turn the burner switch on the right side of the manager to the off position. Turn the system switch on. If there is a call for hot water the system circulator will start and while it's running it will vent the remaining air in the boiler. Turn the system switch off and on a few times, which will remove any remaining air. When that's done turn the burner switch back on and open all of the ball valves.

Sounds complicated but it's not and doesn't require any special tools, just test strips for the A/F.

Dapoppa,
Thanks again for the detailed response. I was able to reach the installer of this system and he confirmed that the purple additive was in fact the System 2000 boiler treatment and not antifreeze. Given this information, if I drain and refill one zone of this three-zone system, would I need to add some of this purple additive to restore it to original concentration? Would I add it through the automatic air vent as you suggested for antifreeze?

One quart of treatment is good for 35 gallons of water. I doubt there's that much in your system so you should not have to add any when you're done.