Furnace Troubleshooting Tips


At Wyckoff Heating & Cooling, we understand unexpected HVAC system repairs are inconvenient, and often an update you don’t have in the budget this month. The good news is, sometimes a service call can be prevented with a few simple troubleshooting tests. Before you invest in any major work on your furnace, try these steps first:

  • Check the furnace filter. Dirty air filters are responsible for 90 percent of all furnace problems. They restrict airflow into your furnace, causing it to work overtime in an effort to heat your home. Over worked means overheating, and ultimately will result in the limit switch, a safety control mechanism, to shut off furnace system burners. Take a few minutes to check and replace your furnace air filter. Hit the reset button, and wait 30 minutes to see if your furnace begins to distribute warm air again.
  • Make sure thermostat settings are at “On.” Is the furnace’s blower constantly running? You may have noticed air in your home seems cool, but oddly your home is maintaining its set temperature. Check your thermostat to ensure the fan setting is set to “Auto” rather than “On.” Why? If your thermostat fan setting is set to “On,” the furnace blower will run even when your furnace isn’t heating the air. The air you feel coming out of your vents (when the furnace is not running) will seem cool since it’s at room temperature.
  • Ensure the thermostat is set to “Heat.” The heat switch can easily get moved or bumped during the day. Ensure the set point is at a temperature that will turn on the furnace. Give the furnace a couple minutes to allow the heat to kick in. If necessary, raise the setting five degrees. The higher temperature will kick start your furnace to turn on if the heat setting is the source of your issue.
  • Inspect the furnace pilot light. After you have checked your thermostat setting and air filter, check to see if the pilot light is out on your gas furnace. There are a few ways you can resolve the issue. First, relight the pilot light. It may stay on after your first attempt and your heating will be restored immediately. If the pilot lights initially, but will not hold a light, there may be an issue with the thermocouple. This is the copper piece the pilot light typically touches. The thermocouple may need adjustment or replacement. Contact a Wyckoff technician for assistance.
  • Inspect the gas valve. If the pilot refuses to light, check to ensure gas is flowing into the furnace. You can do this by inspecting the gas valve switch, which should be within six feet of the furnace. The switch should be in the “On” position, or parallel with the gas supply pipe. If you confirm the switch is on, but still cannot get the pilot to light, clean the pilot to allow gas to get through.
  • Open registers. Wyckoff advises no more than 20 percent of heat registers should be closed at one time. Closing off too many passages can result in high resistance and unnecessary heat build-up in the furnace. It is ok to close some registers to reduce energy costs, but keep the 20 percent rule in mind.
  • Check thermostat batteries. Some thermostats are wired to the house’s electrical system, while others use batteries. Know how your thermostat is powered. Check to see if the low battery symbol is illuminated. However, even if it is not, you may still wish to check your batteries in case the warning light has gone out altogether.
  • Locate the circuit breaker. Visit your home’s circuit breaker panel and look for blown fuses or tripped circuit breakers. If the furnace switch is in a different position than the others, you may have discovered the issue. Simply switch the circuit to the off position, if it isn’t already there, and then flip it back on. Check both the main electrical panel and any secondary subpanels that supply power to the unit. If the circuit blows again, there may be a short in your electrical system, and you should contact an electrician.
  • Flip the furnace power switch. Often mistaken for a regular light switch, the furnace switch is located either on the unit or on a wall nearby. The switch may be unlabeled, but once you uncover the location, turn the switch to the “On” position and wait for the furnace to begin working.

Heating issues can be frustrating and confusing. If you have tried these troubleshooting steps and are still experiencing a furnace failure, contact Wyckoff Heating & Cooling immediately.