I just went through this hair pulling problem. I changed my filter and little to no water pressure. No its not air in the lines ,No its not freezing lines,No its not low water pressure in my house. If you put your old filter back in and it still has no pressure ,its no the filter "makes sense". I shut of my water line to my fridge and removed my filter. I looked inside and saw 2 small little tits that have an "X" marked shape, The centre one was filly out but the outside one was partially out. I you depress both of them they bounce back cause of spring pressure, The correct term "Check valves" possible one way . Any ways what i did was push the one that you think is not fully extended in and out maybe 20- 25 times with a long screw driver or a coat hanger. If you have a long pair of needle nose pliers handy grab the "X" valve and push in and out while turning side to side at the same time"keep in mind this is a plastic valve and could be damaged very easily" Hope this helps. Install your filter and turn water supply back on , this should do the trick.