Your description of how you beld out the zone wasn't 100% clear so make sure you follow the steps below for a standard zone with no splits anywhere, including at the radiators:
- Turn off the power to your boiler
- Turn off the return line valve and hook a hose to boiler drain above the valve you just turned off and run it outside or into a bucket. If into a bucket, you may have to empty it a couple of times . IMPORTANT: This is the drain on the zone pipe and not on the boiler.
- Manual add water to your boiler using the lever on the automatic water feed until the water pressure is 20-25 PSI. IMPORTANT: Be sure to watch the water PSI the whole time and don't let it get above 25 PSI as the relief valve will open at 30 PSI. If it goes above 25, release the lever.
- Once it reaches that range, turn on the boiler drain that the hose is connected to and run it until you start to hear or feel air come out of the line. If the PSI drops below 15, turn off the drain and let the pressure build back up and then turn it back on again.
- Run it until the air stops. If there is no air after a reasonable amount of time, turn the valve back on (the one you turned off earlier next to the drain) for a few seconds to bleed between the boiler drain and boiler and then release the automatic water feed lever and turn off the drain.
When you're all done, bring the PSI down to 12 PSI (open the drain valve to release pressure if needed) and turn the furnace back on. Keep in mind that the pressure will rise once the water heats back up to normal temperature, if you happen to look at it later.
Keep in mind that the boiler value you're dealing with is the one on the zone pipe and not on the boiler.