5 Reasons Why Your Gas Furnace Won't Come On

Few things are more annoying than trying to start your furnace on the first cold day of the season only to find that it won't come on. If you are faced with this predicament, the first thing that you should do is press the reset button on the furnace. If it still fails to operate properly, one or more of the following five situations may be the culprit:

The Thermostat is Faulty

The thermostat is the "on" switch of your furnace and one of the most common causes of a failure to produce heat. There are several reasons why the thermostat may be the culprit, including:

  • The thermostat's circuit breaker is switched off.
  • The pilot light isn't lit.
  • There is dust buildup in the thermostat.
  • The battery is dead.
  • The heat setting is set lower than the actual temperature of the home.

After checking the breaker and the pilot and making sure that they are in turned on and working properly, you can open the covers of the thermostat and use a small, soft brush to remove any accumulated dust. Most thermostat covers snap or clip on and off easily, allowing you to access the inner workings. Also, although modern furnaces don't require a battery to function, most have them as backups for power outages. A dead battery during a power outage could cause the thermostat to revert to its default setting.

The Gas Valve is Closed

This is likely to be the case if you are trying to turn your furnace on for the first time after it's been off for several months -- it may have gotten shut off when spring and summer temperatures became warm enough so that turning on the heat wasn't necessary. Even if this isn't the problem, knowing where the valve is on your gas furnace is a good idea in case you ever need to shut the gas off in an emergency.

The Air Filter is Dirty

An air filter that's clogged with dirty, dust, and grime can cause your gas furnace to overheat and stop working. Replacing the air filter is an easy job that you should be able to do yourself after consulting your furnace's maintenance manual. It's also one of the routine jobs that furnace care professionals do as a part of scheduled maintenance. Many homeowners find that having their furnaces professionally cleaned and maintained in autumn is the best way to keep their homes cozy and warm all winter long without unpleasant interruptions.

The Pilot Light is Faulty

There are several reasons why a pilot light will simply fail to ignite. Ruling out the possibility of a faulty thermostat, these reasons include:

  • The wiring is loose or corroded.
  • The gas line leading to the pilot light is obstructed or bent.
  • The pilot light orifice is clogged.
  • The flame sensor is faulty.

Cleaning out the pilot light orifice is something that homeowners can easily do using a clean, soft rag, but wiring issues are best left to professionals unless you are very adept at dealing with household wiring. If your furnace is one of the newer ones with an electronic flame sensor, you may be able to replace it yourself if necessary. However, if in doubt, it's always best to call in professional heating contractors for even small furnace repair tasks.

The Outdoor Vents Are Blocked

Another reason why your furnace may fail to function is that the outdoor vents have somehow gotten blocked. If you've just experienced your first winter storm of the season, snow and ice may be the culprit. Fallen leaves and other yard debris can also pile up and block vents, so be sure to check them prior to turning your furnace on for the first time in autumn or winter.

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