I have expanded my system (more and bigger radiators over teh years) and recently the system is losing pressure, I am sure there are no leaks. When the system is fired up all is good and the pressure rise to 1.5 and then falls back when cold to .5. After about 2 days of this the pressure is down to 0. Could I need a bigger exapnsion tank to cope with the bigger system to allow for expansion without losing all the water. Also when I set my pump to 3 the pressure increase and I lose water faster out of the system.