Harold Kestenholz
You have lost the seal of your system against the loss of air. When you have the type of system with an expansion tank that must be drained, it is called an air control system. If you have automatic vents or other openings in the system, or change to a high-head pump on the return, you can start to lose the air that must return to the expansion tank. Your system was not well-controlled in the past because you had to drain the tank twice per year, now the problem has accelerated.
