I agree with everything this post says, but would like to add, if your furnace does not work, before you panic, check the batteries in your thermostat and check your filter. These are two very simple things that cause issues that you can easily fix yourself.

1. Total loss of heat Suppose you turn the furnace on and the heating system gives you no response; you could say there is a total loss of heat. The problem could be as simple as a blown fuse to fu…

Source: Common Heating Problems