Ours is a 2 level house (1995), both levels heated by the same furnace ( YORK Multiposition Gas-Fired Furnace MODEL P2MP 32-112 MBH OUTPUT) . We have two digital thermostats (Hunter Programmable type) located on each floor. We were out for a few days and when we came back the lower level is getting heat at all. When we set the Thermostat to Heat, all the vents start to pump air, but the air is kind of cold.
Upstairs, the vents pump warm air and the set temperature is maintained correctly. I am puzzled because it is using the same furnace! We never had heating related problem before. What should I be looking for?

You have 2 zones. The one zone is not operating and has had a component failure. Could be the damper motor or controller. Call for service.