Flush a closed hot water boiler system

[bednar7946]

Hello all, so I moved into a house that had an old outdoor boiler that heats my home and domestic hot water. Its connected through an heat exchanger to the water heater, and my oil furnace. 1" pex tubing was run through a modine heater that heated the basement. Found that leak on a sunday evening at about 11 pm. Had to remove the modine and just direct connected the pipe and bypassed the modine.
I have since, bought a more efficient outdoor wood boiler, and purchased a new modine heater. I was encouraged to flush the "system" before circulating the old water in the pipes into the boiler. My question is, should I install the new modine before, or after flushing the system. Or rather, will it damage the modine to try to flush it after installing it? Thanks for any help.
P.s. my old man was a master plumber. And he died last year. Go figure.

 

[frodo]

flush it first
then after connection of new equipment,you will flush it as you purge the air from the system

 

[bednar7946]

What is the best way to purge the air?

 

[frodo]

depends
do you have an air seperator above the expansion tank?
if not
get some tubing and connect [high points in system] to the air vents on the radiators. the tubing out a window
turn the make up water on. and let the pump circ the water over night
as it circs, it will force the air to the top where you are purging.