I have been having problems with air in the system ever since I converted from gravity HW to a pumped system with 2 valves (1 CH & 1HW).
To overcome the air problem I have done some re -piping and put in a ventair device.
The Feed from the top of boiler rises vertical through the ventair device , the pump is on a tapping on the side of the ventair and the cold feed is between the Ventair and the pump (The vent, cold feed and pump are all within about 6 inches of pipe) The pumped feed then splits to HW and CH circuits. The returns are through the two valves to the bottom of the boiler.
I have just filled and bled the system. Running the pump (without heat)what is happening is that the water is pumped through the heting system and the bolier then up the vent pipe to the tank, down the expansion pipe and back into the pump. (The expansion tank does not overflow)
Altering the speed of the pump has no effect on the problem.
Where do I go from here?????