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What To Do if Your Furnace Won't Turn On

When the weather is chilly in Louisville, KY, it can be stressful to discover that your heating system won’t turn on to warm your home. While your first instinct may be to run to the thermostat to start troubleshooting settings, many furnace troubles stem from deeper problems within your HVAC system, and you could have problems with your blower, heat exchanger, heat pump, electrical circuits, or other delicate systems.

Fortunately, by knowing how to search out problems, you can save yourself time and energy—and know when to call in the help of a professional HVAC technician. Jarboe’s Heating, Cooling & Plumbing is committed to empowering homeowners with the knowledge they need to keep their heating and air conditioning system in top condition. Use this guide to learn what to do when your furnace won’t turn on, and remember, you can always place a service call with their team of HVAC technicians.

1. Thermostat Not Receiving Power

Your thermostat is an electronic appliance that requires power. The system uses electrical signals to relay information from the temperature sensors to your furnace, indicating when to turn on and shut down. While many thermostats are hard-wired and receive power through your home’s circuit breaker and city electrical grid, others relyhard-wired on batteries. If your furnace isn’t turning on, check your thermostat to make sure it seems to be receiving power.

  1. Inspect the Display: Check to see if your thermostat is displaying anything at all on the screen. If the system isn’t receiving power, the viewer screen may be completely blank, and it could signal a power problem.
  2. Replace Backup Batteries: If your thermostat screen is blank, try replacing the backup batteries. Sometimes, hardwired thermostats with issues like tripped breakers may rely on backup batteries, draining the power source. If replacing your backup batteries turns on the thermostat, you may have an electrical connection issue within the thermostat’s hardwiring. Check to see if there is a tripped breaker in your circuit box and reset it. If your unit is hard-wired but there aren’t breakers to reset, consult with an HVAC technician. Wiring may be corroded, damaged, or misplaced.

2. Incorrect Thermostat Programming or Settings

If your furnace isn’t responding, it could be a problem as simple as the settings on your thermostat being incorrect. Since your thermostat is responsible for sensing the ambient temperature of a room, a system that isn’t set up properly could trigger your furnace to switch on or turn off when you aren’t expecting it. Check these two important settings when you inspect your thermostat.

  1. Heat Mode: Double-check that your thermostat is set to “HEAT” and that the set temperature is higher than the current temperature. Make sure your furnace isn’t on “COOL,” HOLD,” or “VACATION” MODE.
  2. Time, Date, and Temperature Settings: Make sure the date and time are correct on your thermostat. Also, check to see when your system is programmed to shift to a new temperature. Since many people program their thermostats to heat less often when people are typically away during the day, you may need to update the scheduling within the thermostat to accommodate your current heating needs.
  3. Hold Mode: When you are home and need to adjust the regularly scheduled heating your thermostat is set up for, use the “HOLD” mode feature. This button, switch, or setting is designed to temporarily pause the scheduled heating of your home to accommodate your current requests. When you leave the house or want to end the interrupted cycle, turn the “HOLD” setting off to prevent wasting energy.

3. Furnace Not Receiving Power

Like any other appliance in your home, your furnace needs a power source to function properly. Gas furnaces rely on both an electrical connection and a gas source, or your system will not turn on. If your heater isn’t receiving power, it may not turn on, warm your home, or exhibit any “signs of life.” Here are a few things to check if it seems like your furnace is not receiving power.

  1. Breaker Box: Inspect the breaker box within your home to see if the circuit breaker governing the furnace is tripped. Tripped breakers may be ever-so-slightly out of place, so look for small inconsistencies with the orientation of the paddle. Reset the paddle by flipping it one way and then moving it the other if it appears tripped.
  2. ON/OFF Switches: There are physical on/off switches on your furnace. Make sure these switches have not been flipped.
  3. Fuses: Conventional furnaces also contain fuses. Power overloads, replacing the thermostat without cutting power first, and wiring problems can burn out these fuses, halting power to your furnace. Check the fuses within your furnace to see if they need to be replaced.
  1. Switch Off Electrical Power at the Circuit Breaker
  2. Open your furnace’s access door to find the circuit board. Find the fuse. It may be a bright color, and it will be small, plastic, and removable. Many are bright colors.
  3. Take the fuse out and inspect it with a flashlight. Damaged fuses may appear burned or contain broken internal filament.
  4. Take the fuse with you to the home improvement store to find an appropriate replacement. You can also find furnace fuses at auto parts stores. Replace the fuse with a version that has the same amperage.
  5. Close the access door, flip the power back on, and adjust the thermostat to see if your system turns on.
  6. If the furnace turns on but the fuse blows again, there could be an electrical problem within your system. Call in a professional HVAC technician to diagnose and repair the problem.

4. Gas Line: Natural gas furnaces rely on a constant flow of fuel to continue to run. If you have this kind of furnace, check to see if the gas valves are open. Open valves should run parallel to the gas pipe, and closed valves will sit perpendicular to the line. Open the valve if it is closed.

If the valve is open, but you don’t think your system is receiving fuel, contact your utility provider to see if there are utility disruptions close to your home. If there are no disruptions and the valve is open, there may be issues with your furnace that are prompting your system to stay turned off. For instance, draft inducer motor, pressure switches, and circuit board problems could prompt your system to stay off, even when everything else is working properly.

4. Access Panels Ajar

Furnaces are designed with many fail-safes to protect homeowners. One such safety feature turns off the furnace if any access panels are out of place. If your furnace isn’t powering on, check the exterior cabinet carefully to see if you can spot panels that are out of place, missing screws, or that appear damaged in any way. Push panels back in place, and replace any missing screws to see if that triggers your furnace to run properly.

5. Furnace Not Igniting

If your furnace is turning on but not creating any heat, you may have a furnace ignition problem. If the blower turns on and runs, but the air coming out of the vents of your home is cold, the ignition could be to blame. Here are a few common ignition problems and how to resolve them.

Pilot Light Off

Pilot lights can go out due to system issues, drafts, or even tripped failsafes inside your furnace. If your pilot light isn’t working, your furnace will not be able to ignite the flames of your furnace, and your system won’t heat. To light your pilot light, use your furnace owner’s manual and follow the directions closely. Here are a few guidelines for relighting your pilot light.

  1. Remove the furnace access panel by unscrewing the hand screws. Find the pilot light assembly inside the furnace. The system should have a reset switch. Turn it to “OFF,” and wait 5-10 minutes to give the gas time to dissipate.
  2. Turn the Switch to “PILOT” to Trigger the Flow of Natural Gas
  3. Hold in the reset switch and use either a match or lighter to relight the pilot light. Try to do this step relatively quickly so too much gas doesn’t dissipate around the furnace. Keep a hold on the switch until the pilot burns steadily.
  4. Release your hold on the switch and watch the pilot light. If the flames go out again or seem to struggle, check for drafts. If the pilot light won’t stay lit, place a professional service call.

Electronic Ignition Dusty or Dirty

Electronic ignitions can become dirty from soot buildup on the ignitor. Eventually, the entire ignition sequence will stop operating, which keeps the system from starting up. Typically when this happens, the furnace emits a clicking noise, but the furnace doesn’t turn on. Cleaning the ignition can help, but it is crucial to be as careful as possible since these elements are delicate and can be damaged easily. If the ignition sequence does become damaged, it will need to be completely replaced.

  1. Cut the Power to Your Furnace by Switching Off the Breaker That Controls Your Furnace, or by Using the On/Off Switches on the Side of Your Unit
  2. Turn Off the Natural Gas Line Valve by Your Furnace by Turning the Handle Until It Is Perpendicular to the Supply Line
  3. There Is Another Access Panel to the Burner Compartment. Remove the Panel Cover
  4. Ignitor components are ceramic with wire connections at the ends. Use compressed air to dust off the ignitors. Maintain a distance of at least a foot.
  5. Put the Panel Back in Place, Restore Power and Gas, and Turn the Furnace Back On

If the furnace turns back on, you may have resolved the issue. If the ignitor is broken, the ignition sequence may need professional repairs.

6. Furnace Shuts down and Won’t Turn Back On

If your furnace short cycles, or turns on but then turns off quickly, there may be deeper issues at fault. Here are a few reasons your furnace may be turning off.

Grimy Air Filters

When air filters become dirty and clogged with grime, they prevent normal airflow from within the furnace. This simple problem can allow too much heat to build within the heater, which can damage the furnace components. Check your filter and replace it whenever it appears dirty.

Dusty Flame Sensors

The furnace flame sensor detects when a flame is present while gas flows through the system. If it becomes dirty with soot from combustion, it may not correctly sense the flame and shut down the furnace for safety incorrectly, even though everything else is working properly. To clean the flame sensor, follow these troubleshooting steps:

  1. Turn Off the Power to the Furnace by Shutting the Valve and Flipping the Breaker
  2. Remove the Access Panel
  3. Remove the Flame Sensor. This Step Requires a ¼ Inch Hex Wrench. In Some Furnaces, You May Need to Disconnect a Wire to Access the Area Better
  4. Lightly Rub the Sensor Rod With Light Grit Sandpaper. This Step Removes Carbon and Soot
  5. Clean the Sensor With a Cloth by Wiping It Gently
  6. Reconnect Any Wires, and Then Reattach the Flame Sensor
  7. Replace the Access Door and Turn Back on the Power. Open the Gas Valve

When to Call a Professional HVAC Technician

Anytime you try to troubleshoot your furnace and it isn’t working, it’s important to call in the help of a professional. Here at Jarboe’s Heating, Cooling & Plumbing, we are always here to help. Whether you experience a sudden heating failure or your system needs a routine tune-up, we can help. Give us a call to help you to get your HVAC system on track.

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