Hi I have a gas heater in the basement that will not blow out any warm air. I was on here a few weeks ago and changed the thermostat and that seemed to make the heat blow warm air. I was gone all weekend and turned off the heat. Came back and naturally it was cold thermostat said the house was 44deg. I turned the thermostat to heat, it blew warm air for about 15 minutes then cold air. Kept turning thermostat on and off throughout the night and nothing but cold air blowing out of the vents. Please advise on what to do. In Pennsylvania in the 20s outside and I can't have the house this cold again tonight, I have three little girls. Do I have to reset something? I am trying to avoid spending a ton of money for a service call if possible. Thank you so much. Pics following.

I have a First Co. 36MBXB-HW system (a unit in my attic and one in the basement) and a New Yorker boiler. Last week, I turned on the heat on my second floor, it was about 10 degrees outside, and it only blew cold air. My heat on the first floor worked fine. I thought it might be the Grundfos circulator pump, which has failed before and I've already replaced once for each floor. Bought a new pump, installed and it still blew out cold air. A few days later, the temp went up to 55, so I turned on the heat to the 2nd floor, and it blew out warm/hot air. Yesterday, I turned the heat on to the first floor, and it was blowing cold air. Heat on 2nd floor still works now, but first floor is blowing cold. I cleaned out the air filters in both units, but that didn't fix anything. I doubt its the circulator pump because of what happened with the 2nd floor. The temp outside is 25 degrees. Not sure why heat doesn't come on during coldest temps, or how to repair.