98 Chevrolet Astro Van overheating

Not a great mechanic but tryn to troubleshoot cheap stuff before I take anywhere. Girlfriends Astro Van ran hot two nights ago..It was 10 degrees due to the polar weather deal and she left work at 1 am and drove about 7-8 miles and it redlined on the temp gauge so she pulled over and I picked her up. Drove it the remaining 5 miles the next day but temp starting getting really hot when pulled in driveway..She has had a very small leak for over a year and tops off the coolant every 5-6 weeks so its a small leak..Anyway, shes just been using water so I thought maybe it just froze up with the dramatic drop in temp for first time this winter and probably has more water than antifreeze in it at this point..I heated it up in my garage for a day, drained all the antifreeze/water out and flushed it with hot water and then refilled with just water to let it circulate and check for leaks or if drain/freeze plugs had came out.. No leaks anywhere but just in the ten minutes I had it idling temp went up to 240 in 10 minutes..Its 50 degrees outside also..So obviously the water isn't circulating, I'm thinking possibly the water pump although it was replaced last summer, is there anything else I could check first? Someone had mentioned I may need to bleed the air out of the radiator or something like that as its lost its prime or something. Anyway, just asking for ideas, or even could the freeze have caused the thermostat to malfunction or stick? Any help is appreciated. Thanks