Indirect Hot Water Tank Replacement Help - Boiler Loop

I have a HTP SSU-30 SuperStor 30 gallon indirect hot water tank that is leaking and needs to be replaced.


I'm looking at it and I know how to flush and fill the tank on the cold water side of the system, but right now the only thing I'm working out is how to drain and fill the boiler line that heats the water.



I have a Triangle Tube Solo 60 gas boiler. The piping arrangement is hard to get in all of one shot, but I've attached an overview. Cold supply comes from the right, through reducing valve, jogs down and goes into cast tee with boiler return, comes out of boiler upper center, goes through air separator/expansion tank, then two circ pumps (leftmost is the circ pump that serves the hot water tank). There are ball valves that isolate the line to the hot water tank.


It looks like I can isolate the boiler lines in/out of the heater, drain the coil down with the spigot on the tank, and remove the tank. I'm just trying to figure out how to purge the air that will be in the boiler heater coil after installation, or does that just get blown out and the air separator handles it?


Thanks for your help!