If your gas furnace has suddenly stopped working -- or worse, has begun to blow cold air -- your first instinct may be to research and order a replacement, or contact a repairperson. However, in many cases, you may be able to repair your existing furnace using tools you already have at home. Performing these repairs yourself can save you time and money, as well as help minimize the chilly side effects of a malfunctioning furnace. Read on to learn more about some common problems you can tackle yourself, as well as situations in which you're better off calling in a professional or replacing your gas furnace.

Troubleshooting your furnace

There are a few questions you can ask to help narrow down the cause of your heating problem.

1. Is your pilot light on?

The pilot light is always the first component you should check when your furnace isn't functioning correctly. In some cases, your light may simply have gone out due to a draft -- your "repair" will be quick and easy. However, if your pilot light continues to die, you may have debris in the tube that supplies gas to the light.

You should be able to remove and clean this tube yourself -- but make sure you've cut off the gas supply to your furnace first, to prevent leaks.

2. Is your furnace blowing only cold air?

If your blower motor is working, but the air coming from your vents is cold, there are a few things you should check.

• Propane or natural gas valve

If this valve is closed, it will block the flow of gas to your furnace, eliminating its source of heat. If your heater begins to blow warm air shortly after you've opened this valve, you've found your problem.

• Circuit breaker controlling the furnace

Sometimes certain heating components are covered by different fuses or circuit breakers, making it easy to trip a breaker without noticing. Check all circuit breakers to ensure that none have shut themselves off (and if your heater routinely flips the circuit breaker, you may want to contact a licensed electrician to upgrade your outlets). 

• Air filter

If your air filter is dirty or clogged with debris, it can prevent the warm air from circulating. Check your filter periodically, and change according to the manufacturer's recommended schedule.

When should you call a professional?

If you suspect your furnace issue is due to a thermostat problem, you'll likely want to contact a certified repairperson. The interaction between a thermostat and a gas furnace can be a tricky one, and a minor deviation from installation instructions can leave you with an inoperable furnace.

You should also contact a technician for furnace repair if your furnace won't turn on at all, and you've eliminated the possibility that this is due to a tripped circuit breaker or blown fuse. Your repairperson will probably need to order and install a new blower motor or switch.