bleeding hot water boiler baseboards
Are you sure you are bleeding air out as opposed to the system's sucking air back in? Verify that you have some pressure in the system and the expansion tank is not full of water. Quick preliminary calibration of expansion tank: empty it of water, then repressurize the system to specifications.
The disadvantages of crab apple trees. In summer, the apples are too sour to pick and eat. In winter the birds come and leave dropping all over the place.