Every couple of years I start getting some leaking from my blow off valve and it is because the bladderless expansion tank ( actually 2 plumbed together totally 60 gallons) becomes waterlogged. I have been told to simply drain and let it repressurize by the water feeder. It seems counter intuitive as this method partially fills the tank. Ideally would it not make more sense to pressurize the tank with air to the systems operating pressure at room temperature thus giving the entire volume of the tank for expansion?