I have a 25-year old boiler that heats the floors at my 7-bay SS wash. I repaired a couple lines that did not pressure test last year. All lines now pressure test just fine. The boiler runs at 14lbs pressure when it is on. With temperatures fluctuating above and below freezing, the boiler kicks on/off frequently. The boiler runs fine when it stays on (its been on constantly for four days now and it?s running perfectly at 14PSI) but when it shuts off for a while then turns on later, I have to add four gallons of coolant each time to get the flow going. I have had to do this almost every time the system starts this season. If it wasn?t off for very long it will start back up but only run around 10PSI (low coolant). Any ideas why this is happening? I tested all lines with compressed air and they all held at 20PSI.