Temperature outdoors -10, Ignitor glowing, and recently replaced,can hear the furnace constantly running but fan only kicking on intermittently and blowing out blowing moderately warm air for a very short time then stops, before bring room up to set temp. Thermostat set at 70, heat inside house is only 60. The furnace is approximately 20 years old. It is a heating/AC unit and services a large 100 year old home.