There are 4 zones in the house and the 4 returning pipes connect to one circulator. One zone (ground floor) doesn't seem to be working in the sense that the pipe is cold between 10 inches into the supply pipe of that zone and all the way past the zone valve to where the returning pipe of that zone converges with other returning pipes.

As a temporary solution, (when I feel cold) I would just shut off the returning valves of all 3 other zones, shut off the valve upstream of the circulator, and bleed the system to get the water pushed through. Hot water would run for 30min to few hours, then the flow would stop again.

Is it a air lock problem or the pressure is not right? Any other permanent fixes? Thanks guys!