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No heat in the house? First checks for a furnace or heat pump

Start with the outside checks you can identify and reach safely: thermostat settings, the furnace power switch and a filter slot meant for homeowners. Follow your model's instructions, and don't open burner, control or electrical panels; anything inside the unit is a job for a licensed HVAC contractor. Written for homeowners in Greenville, Spartanburg, Anderson and Pickens counties.

Published Sources listed at the end Checked against Trane, Carrier, ENERGY STAR, CPSC, CDC, Ready.gov, U.S. Fire Administration, National Weather Service and Piedmont Natural Gas guidance

Safety first

Carbon monoxide alarm sounding, or you suspect carbon monoxide even without an alarm? Get outside to fresh air immediately and call 911; don't stay inside to troubleshoot. CPSC advises not to look for the source, to count heads once everyone is outside, and not to go back in until emergency responders say it's safe. Carbon monoxide is colorless and odorless. Headache, fatigue, shortness of breath, nausea or dizziness can be early signs of poisoning.

Smell gas (a rotten-egg smell)? Leave now. Don't touch switches or valves, and call 911 or your gas utility from a safe place well away from the smell. Don't use the other steps on this page if you suspect gas.

No heat tonight? Start here

  1. Carbon monoxide alarm or a gas smell? Follow the safety box above and skip the rest.
  2. Check the thermostat.
  3. Then go to your system: furnace or heat pump.
  4. Waiting for help? Stay warm safely and protect your pipes.

Not sure which system you have? Check the owner's manual or a safely readable equipment label first. Trane says an HSPF or HSPF2 rating identifies a heat pump, and Em Heat or Aux Heat on the thermostat is another clue. Heat pumps and central air conditioners can look alike. Don't identify the system by whether the outdoor unit runs during a no-heat problem: emergency heat can stop a heat pump's outdoor unit, and dual-fuel systems can include both a heat pump and a gas furnace. If you're unsure, give the contractor the model number you can read safely without opening panels.

1. Check the thermostat first

These checks from Trane apply to a furnace or a heat pump:

  • Mode: make sure it's set to Heat, not Cool.
  • Setpoint: set it above the current room temperature.
  • Fan: on the On setting, the fan keeps running even when the system isn't heating, so the vents can blow cool air between cycles, Trane explains. That alone isn't a fault. Set it to Auto so the fan runs when the system heats.
  • Batteries: if your thermostat uses batteries, replace them.

2. Furnace not working or blowing cold air

  • The furnace power switch. Trane says it often looks like a light switch on the side of the furnace, on a nearby wall or on a ceiling joist. If you can identify it and reach it safely, check that it's on. If it's out of easy reach, has a tag on it, or someone turned it off for service, leave it and call a professional.
  • The breaker. Only if the electrical panel is dry and undamaged, there's no burning smell, and you can identify the furnace's breaker, reset it once. If it trips again, don't reset it again: Trane says that means an electrical issue, so call an HVAC professional. Don't remove electrical covers.
  • The air filter. A dirty filter can make a furnace overheat and shut itself off as a safety precaution, Trane explains. If your furnace has a filter slot or door meant for homeowners, Trane's advice is to turn off the furnace first, then replace a dirty filter with a new one; use the type and size your manual calls for. Don't open other panels to reach it, and if you're not sure, leave it to a technician. ENERGY STAR recommends inspecting filters once a month; how often they need replacing depends on the filter.
  • Vents. Carrier suggests making sure supply and return vents are open and unobstructed, for example not covered by furniture or rugs.
  • Other gas appliances out too? If you already know your gas stove or water heater also won't work, Carrier says the gas supply may be disrupted: contact your gas utility. Don't light another appliance to test the gas supply. If you smell gas, follow the safety box above instead.
  • Outdoor vent pipes. If your furnace has intake and exhaust pipes through an outside wall or the roof, Carrier says to be sure they aren't clogged or blocked. Check only what you can see safely from the ground, and don't take the pipes apart.
  • Pilot or ignition problems. If the pilot keeps going out, the burners won't light, or you're not sure what you're looking at, call a professional. Trane says newer furnaces with ignition problems need a professional evaluation. Don't open burner or control panels, and never try to light anything if you smell gas.
  • Other causes are technician jobs. Trane points to professional help for a failing flame sensor or limit switch and for clearing a clogged condensate drain line.

3. Heat pump not heating or blowing cold air

  • Cooler-feeling air isn't always a fault. Trane notes that heat pumps don't blow hot air like a furnace; they blow a steady stream of warm air. If the house is still reaching the thermostat setting, that alone doesn't show a problem. If the house keeps getting colder, call a professional.
  • Defrost mode. If your thermostat or unit displays Defrost, cool air for a while can be normal. Trane says the system should resume heating once it exits Defrost mode. Defrost doesn't explain a house that keeps getting colder.
  • Thermostat, power, filter and vents. Use the checks in step 1, make sure the unit is powered on, and check a homeowner-accessible filter and the vents as in step 2.
  • The outdoor unit. Trane suggests clearing leaves, debris or snow from the top. Do it from outside the unit: don't open the cover or put hands or tools near the fan.
  • Frost or ice on the outdoor unit. Light frost on the outdoor coil can be normal, because heat pumps have a built-in defrost cycle, Trane explains. If ice stays or keeps growing, the unit makes unusual noises, or the house keeps getting colder, contact an HVAC professional instead of waiting. Don't chip at the ice.
  • Strange noises or a suspected electrical problem: Trane says to contact an HVAC professional.

4. Staying warm safely while you wait

  • Never heat the house with a gas oven or stovetop. Ready.gov and CDC warn against it because of carbon monoxide. CDC also says never to use a portable gas camp stove or burn charcoal indoors.
  • Portable heaters: CPSC advises keeping them at least three feet from drapes, furniture, bedding and anything else that can burn, and plugging electric heaters directly into a wall outlet, never an extension cord or power strip. Turn them off when you leave the room or go to bed, the U.S. Fire Administration advises.
  • Generators: use a portable generator outdoors only, at least 20 feet from the home and away from windows, doors and vents, with the exhaust pointed away from buildings, CPSC and CDC advise. Never run one inside a home, garage, basement, crawlspace or shed, even with doors open.
  • Carbon monoxide alarms: CPSC recommends battery-operated alarms, or alarms with battery backup, on every level of the home and outside sleeping areas. Test them monthly and follow the manufacturer's instructions. See our carbon monoxide alarm guide for what to do if one goes off or chirps.
  • Can't keep the house safely warm? Move to a safe, heated place while you arrange help. Don't rely on improvised heating.

5. Protect your pipes when the heat is out

A cold house can mean frozen pipes. At Greenville-Spartanburg, National Weather Service records show the first freeze of the season has come as early as September 30 and as late as December 14. If the heat is out on a freezing night, see our frozen or burst pipe guide, and know where your main water shut-off valve is.

6. When to call a licensed HVAC contractor

  • The thermostat, power switch, breaker and filter checks didn't bring the heat back.
  • The house keeps getting colder.
  • The breaker trips again, you hear strange noises, or you suspect an electrical problem.
  • The pilot keeps going out, the burners won't light, or a heat pump's outdoor coil stays iced over or the ice keeps growing.
  • It's time for routine service: CDC recommends having your heating system serviced by a qualified technician every year, and ENERGY STAR says it's best to check the heating system in the fall.

7. Before you call

Note whether you have a gas furnace, an electric furnace or a heat pump, the brand and model if you can read them without opening panels, what you've already checked, and any error code visible on an external display or viewing window without opening a panel; Carrier notes that error codes can point to a problem that needs professional service. In South Carolina, SC LLR's Residential Builders Commission provides residential HVAC licensing information and a license lookup. Check that the contractor's current license fits the work, and ask for a written estimate before work starts.

This guide is for information only. We don't do heating repairs or connect calls for heating service.

Sources