Furnace - fan comes on, but no heat
Check for a tripped limit switch. If the furnace ever gets too hot, a limit swich trips, causing the furnace blower to run continuously to cool it off. Some are automatic reset, others must be reset by pressing a button, and some must be replaced. Look in the furnace manual, and it should say how to reset it. Also, look for a diagnostic code on the furnace control board. If there is no fault code, it might be a thermostat wiring problem. G is usually the wire that turns the fan on.