I turned the thermostat up to 80 degrees, and cold air came out of the vents rather than hot air. We still have hot water and the oven still heats up so the gas hasn't been cut off. What's wrong?
if you know that you have gas going to unit then it could be a number of things. it could be a flame rod dirty, roll out safety bad, board bad, pilot valve bad. call a good hvac tech or company out to check it out.