dead zone

Wid

I have one zone on my boiler system that is blocked somehow. While filling the system, 1 zone at a time, by putting a sump pump in a bucket connected to the drain spigot on the return line and pouring antifreeze into the bucket as needed, I closed the valve under the circ pump on the return side, opened the valve to a zone on the supply side and the drain spigot above the circ pump on the return side with a hose aimed into the bucket. This should push the antifr into the zone flushing out all the air in that zone until it is satisfactorally full then I can go to the next zone. But one zone doesn't work, it is blocked. Checking the bleeder valve on that zone down the line revealed no liquid in the line, no antifreeze goes in and nothing comes out. I raised the thumb turn on the taco 219 swetchek but no change. I then removed the thumbturn assembly from the taco... and liquid came out from either direction in the line. Can taco 219 swetcheks break?