There are several possible reasons why your furnace may be running but not providing heat. One possibility is that the pilot light is out or has gone out. If this is the case, relighting the pilot should take care of the problem. Another possibility is that there is an issue with the electrical supply to the furnace. If this is the case, you will need to have an electrician look at it. Finally, it is also possible that there is something wrong with the furnace itself. If this is the case, you will need to call a furnace repair technician.