If your furnace quits working while you're away due to a maintenance issue—such as wear and tear or age of the furnace—your homeowners policy will not cover your for a replacement furnace.
However, if your furnace dies during the colder months, and causes the pipes to freeze, you will have coverage on the associated damages. This is because you maintained heat in the dwelling—which is a requirement for freezing to be covered. The furnace malfunction does not negate coverage under this particular circumstance.
You can also contact your agent to check to see if your specific carrier offers equipment breakdown coverage. This could provide additional coverage for your furnace as well.