I have a hot water boiler heating system in my basement. I have a supply line with a gate valve, then a pressure reducing valve with fast fill. This goes to another gate valve right by the boiler except this gate valve is a 3 way. One way the supply line comes in from the PRV, another way goes to a fill-trol expasion tank and the third way goes right into the loop of the boiler. It is located about 8 inches below the circulator pump that goes into the boiler low and on the side of the boiler. Then I have a pipe coming out of the top of the boiler going up to a Taco Air scoop which has a pipe coming off the top of the air scoop going to a big steel expansion tank hanging from the ceiling of the basement.......Now here's my problem. I filled this sytem the first time when I moved into this house 2 years ago. I remember just opening the gate valve at the beginning of the supply line. I also remember for the next two or three days, going around bleeding the baseboards over and over getting little air every time. Eventually I got all the air out and the system ran fine for two years. This year I emptied the system to repair a leak on the one radiator I have in the basement. I went to fill up the system when I was done. I let the thing fill for two days bleeding the rads every couple hours for two days. I started getting water out of a few rads, but 2 rooms or so (all on the main floor, I have no upstairs also) would not give me air or water and the boiler gauge only ever went up to about 7 pounds maybe 10. I recall my system having 12-15 pounds previous years. So I figured it must be the PRV and I went out today, bought a new one (B&G FB-38), and put it on. I made quick work of this project and have no leaks. Now when I turn on the supply I still get the same crap and when I flip that fast fill lever up it doesn't really do anything. Or at least it doesn't sound like it is. I know the pressure in the supply line is good as I checked it when I had the PRV off. Plenty of water comes out when I begin to open the gate valve just before the PRV. I am stumped. Why do I have 2 expansion tanks? (small bladder one, low on the system and big steel one hanging from rafters) There is about 14 pounds of air in the small bladder one. The big steel one is never over full of water. I feel as if that damn 3 way gate valve, that has the small expansion tank, supply line, and main heater loop connected to it might not be letting water through it. I don't what this part is called or if it goes bad or gets clogged. But again, I remember this system taking forever to fill up with water before. Anyways, if anyone can help me I would be very appreciative. BTW This system is old. House was built in 1951, the boiler, I believe, is a 1970. I am going to sleep and goto work tomorrow and hope when I come home I get massive amounts of air out of the rads, but I don't know. I hope it works because I froze my arse off this morning. It got down to 32 degs here last night in Chicago. Sorry for all the writing, but I hope I explained the system good enough. Here is the order one more time Supply, Gate Vale, PRV, 3 Way Gate Valve thingy w expansion tank, with third connection into Low Pipe on Boiler, Boiler, Boiler High Pipe to Taco Air Scoop w Branch off of top to Steel Expansion Tank, through the Taco around the house to all Rads, then to the lower Boiler Pipe with a Circulator Pump on it. That makes the whole circuit. Thank you in advance.