If you don't have automatic air bleeders installed in the system you consider getting some. All Hydronic heating
systems should have these. Any good plumbing
supply will have them. They are installed in a tee fitting facing up. A float and a weight open the bleed valve by gravity when air is present. When fluid replaces the air the float rises and closes the bleed valve. You may never get the air out without some of these at various spots.
You should not need code reading software
. The thermostat should have an LED that blinks when the system shuts down. The number and duration of blinks will tell the reason for shutdown.