Furnace not turning on? Try these 5 DIY tricks.

Furnace not turning on? Try these 5 DIY tricks.

Furnace trouble can often be fixed with one of these five handy tricks.

Key tips to remember

  • Check the power
  • Check the thermostat
  • Check the gas
  • Check the pilot light and ignition sensor
  • Check the air filter

You knew it was coming. You tried to resist it for as long as possible. You’ve piled on the blankets, relied on fireplaces or space heaters, and attempted to beat your own cold-temperature records, but it’s about that time. There’s nothing to be ashamed of. We’ve reached that point in the year when most of us give in. However, when you finally decide your house needs warming up, but your heat won’t turn on, it’s easy to panic. It was stressful enough being this cold for this long while you tried to talk yourself out of using the heat, and now flipping on your furnace switch produces no results? It’s infuriating.

Is your heater not turning on? Well, just try to remain calm and relax, and before you start calling for professional help or Googling stuff like “fix heater,” “my heater is not working,” or “why won’t my furnace turn on,” we’ve put together some of the most common fixes for times when your furnace won’t ignite. They could save you a panic attack, as well as quite a few dollars on all that professional help. Even if none of our suggestions work, you’ll still feel a little better having tried to do all you could as a nonprofessional furnace-fixing homeowner before calling in the pros. We would.

Power check

No power to the furnace? Whatever fuels your furnace, it has no hope of turning on in the first place without power, so this is a good place to start. Check your breaker box first, making sure the breaker powering your furnace’s circuit hasn’t tripped. Then make sure the power cord is in good shape and that the power switch — which you can find near the unit, if not directly on the unit itself — is set to the “on” position, usually flipped up rather than toward the floor. Sometimes it’s not labeled and resembles a light switch. If you spot burn marks anywhere, you could be dealing with electrical damage and might need professional help. Oh, and one more thing: Sometimes furnaces don’t even have a switch, so don’t go crazy trying to find one. If it’s not there, it’s probably not there. No worries. Move right along to our next step.

Thermostat check

Thermostat not turning on the heat? If you have power at the unit and have made the related checks above, your next step is checking the thermostat again. We say again because we know that your thermostat is where you tried to turn on the heat in the first place. If your furnace won’t turn on with thermostat power established, make sure your thermostat is getting power. Check the wires going into the back of the thermostat to make sure they’re all still connected and haven’t been knocked loose inadvertently. Look for any error code on your thermostat’s display, and then check the manual (on paper or online) to find out what the code means. Make sure the display is lit and that all functionality is retained. Check the settings to be certain that someone hasn’t set the heat to be off for some reason. If this is the case, refresh the settings and again set the thermostat to heat. Your heat should be coming on momentarily, and you should be able to set your preferred temperature. If not, you may need a new thermostat.

Gas check

Verify that your gas is turned on and coming into the house by checking the outside shutoff valve, typically located on a side of the house facing the street. The “on” position for gas flow is when the valve handle is aligned parallel with the gas pipe. When it’s perpendicular, it’s off. Once you’ve established that the gas is on, it’s time to move to the house-side valve located inside near the main line input from the outdoor gas pipe. Make sure that this valve is also open and parallel to the pipe. Once you’ve established gas flow with both of these main valves, check a couple of different gas-powered appliances to see if you have a problem with only the line going to your furnace. 

If it looks like multiple appliances are still getting their gas supply, make sure the furnace is getting incoming gas too, and that no inline shutoff valves have been turned off at or near the furnace unit. These valves, like the outside and main house valves, are open when turned parallel with the gas pipe itself and in the “off” position when turned perpendicular to it. Your furnace will have one of these third valves, typically within about 6 feet of the unit, which could’ve been turned off accidentally. If at this point you still aren’t having luck with the furnace, there could be a service interruption or construction in your area, or perhaps a problem with an unpaid bill or clerical error on your account, so it’s worth checking with your gas company. However, if at any time you smell gas and suspect a leak, don’t hesitate to evacwwwe the home and call the gas company.

Pilot-light or ignition-sensor check

If your HVAC won’t turn on, and you feel neither heat nor moving air, one of the most common problems is the pilot light has gone out. Pilot lights can be blown out by momentary gusts of air caused by any number of things. Newer systems make this more unlikely, and the latest models of many gas systems don’t even have pilot lights anymore. You should be able to relight yours without much trouble. If it stays lit, you’re in good shape. If not, you might have an assembly or ignition-sensor problem. If your sensor is malfunctioning, the system won’t recognize the light and will impede the flow of unburned gas accordingly. Either way, you’ll have a problem getting your furnace to heat your home. 

Ignition sensors aren’t difficult to replace, though. If you turn off the power and the gas flow, and then remove the front panel, you’ll find the ignition sensor near the burners. What you’re looking for is a little porcelain doodad with a metal rod near the pilot light. You should be able to unscrew and pry out the sensor with a screwdriver, clean it by removing any buildup with steel wool or a pocketknife, and replace it. But be careful because it is delicate, and you don’t want the rod to detach. Reverse your steps and see if the furnace fires up this time. It could take a while, depending on how long it takes the gas to reach the pilot light, particularly if this is your first time lighting it for months. Wait an additional half-hour or so to give the system time to warm up again.

Air-filter check

Plan on replacing your furnace’s air filter at least once every three months, whether you’re having trouble with the system or not. Reduced airflow due to the buildup of dust, hair and dirt can place a real drag on the efficiency of your HVAC unit and prevent heat from  distributing effectively. A dirty filter can also lead to heat buildup in the exchanger, which can engage a limit switch, automatically shutting down the system to prevent overheating. Changing the filter is as simple as finding the airflow point at which air flows into the furnace. Remove this filter, noting its measurements, and replace it with a new one, taking care to follow the arrows printed on the filter indicating which side should face the furnace. If you have trouble with this or any of our other four steps to take when your furnace won’t turn on, feel free to contact a professional.

Thanks for reading our quick DIY suggestions on how to fix a furnace. If you’d like to dig into this issue a little deeper, check out our furnace maintenance checklist and learn how to make your HVAC system more efficient. While you’re here, you may also be interested in reading about the true costs of replacing a radiator, assessing the risks of buying an older home, or any number of our other handy, helpful posts about various issues in and around your home.

The information in this article is intended to provide guidance on the proper maintenance and care of systems and appliances in the home. Not all of the topics mentioned are covered by our home warranty or maintenance plans. Please review your home warranty contract carefully to understand your coverage.

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