Your method depends on where the Auto feed (anto make up) line i

If your auto feed (anto make up) line is connected at the supply side of the boiler, your method will work. However if your auto feed (anto make up) line is connected at the return side of the boiler, your method will not work. Because the make up water will feed the space in the boiler when water drains out.

If there is an auto feed (anto make up) line in your heating system, usually you should not have air in the heating pipes. The reason you had your problem was your pressure regulator is set too low. The regulator pressure has to be 5 to 7 psi over the system pressure at the feed point that your water can feed normally. This is the problem for the auto feed (anto make up) line connected at supply side. If you connect your auto feed (anto make up) line at the at return side of a boiler, you do not have this problem because at the return side, the system pressure is closed 0. So you only need to install a 7 psig water pressure regulator.