It's winter. You hear your gas furnace cycle on but the vents are only blowing cold air. What is the most common cause for this?
Answer The pilot light has gone out or your air filter needs to be replaced.
Your furnace may be blowing cold air because the filter is too dirty. A dirty air filter blocks airflow over the furnace's heat exchanger, causing it to overheat. If the pilot light isn't lit, then the furnace's burners won't light, meaning no heat.
Asked by Cliff Johnson · Last updated 7 months ago · 188.5K views