It's a cold morning and the furnace isn't running. Before you assume the worst, know that a no-heat problem sometimes comes down to something simple: a thermostat setting, a tripped breaker or a clogged filter.

Central Ohio's first real cold snaps are when a lot of furnaces get tested. Here are eight safe checks you can do in a few minutes, plus the signs that mean it's time to stop and call.

One rule before you start: if you smell gas or a carbon monoxide alarm is sounding, skip this list and go straight to the safety steps under "When to Stop and Call."

8 Checks Before You Call

1. Check the Thermostat

Make sure it's set to Heat, not Cool or Off, and that the set temperature is a few degrees above the room temperature. If the screen is blank or dim, replace the batteries.

2. Check the Breaker and the Furnace Power Switch

Look in your electrical panel for a tripped breaker labeled furnace, HVAC or air handler, and reset it once. Near the furnace there's usually a switch that looks like a regular light switch. It's easy to flip off by mistake. Make sure it's on.

3. Make Sure the Front Panel Is On Tight

Most furnaces have a safety switch behind the lower door panel. If the panel is loose or not seated right, often after a filter change, the furnace won't start. Press the panel firmly into place.

4. Look at the Air Filter

A badly clogged filter chokes airflow. The furnace can overheat and shut itself off as a safety measure, and some will stop trying to restart. Put in a fresh filter with the airflow arrow pointing toward the furnace.

5. Check the Gas Supply

Find the gas valve on the line going into the furnace. When it's open, the handle runs in the same direction as the pipe. If you find it closed and don't know why, call us before opening it. If your other gas appliances aren't working either, the problem may be the gas supply, not the furnace.

Many rural homes in the townships outside Delaware and Marysville heat with propane. Check the tank gauge. If the tank ran empty, call your propane supplier, since the system may need to be checked before appliances are relit.

6. Check the Condensate Drain and Float Switch

High-efficiency furnaces make water as they run. It drains through a small plastic line, sometimes to a condensate pump. If it clogs or freezes, or the pump's float switch trips, the furnace shuts down to prevent a leak. Look for water around the furnace or a full pump reservoir. If the line runs through a cold garage or crawl space, it may be frozen.

7. Clear the Outside Vent Pipes

If your furnace vents through one or two plastic pipes on an outside wall, go take a look. Snow drifts, ice, leaves and bird or wasp nests can block the intake or exhaust, and the furnace will shut itself off. Gently clear snow and debris from the openings, but don't push anything into the pipes. If they exit through the roof, don't climb up. Call us.

8. Read the Error-Code Light

Many furnaces have a small light, often visible through a window in the lower panel, that blinks a code. Count the blinks and match them to the chart, usually on the inside of the furnace door. Read it before you remove the door, since opening the panel cuts power and can clear the code. Write the pattern down for us.

Turning the furnace power switch off for a minute and back on can clear a lockout once. If it locks out again, call.

When to Stop and Call

  • You smell gas. Leave the home right away. Don't flip light switches or use your phone inside. Call your gas utility or 911 from outside, and don't go back in until they say it's safe.
  • A carbon monoxide alarm goes off. Get everyone, pets included, outside into fresh air and call 911. Don't run the furnace again until it's been checked.
  • The breaker keeps tripping. One trip can be a fluke. A second trip points to an electrical problem that needs a technician.
  • You hear clicking but see no flame. If the ignitor clicks or glows but the burners never light, or they light and shut off within seconds, the cause could be the ignitor, flame sensor or gas supply. Repeated restart attempts won't fix it.

Staying Warm Until We Arrive

  • Use space heaters safely. Plug them directly into a wall outlet, not an extension cord or power strip. Keep them well away from curtains, bedding and anything that can burn, and turn them off when you leave the room or go to sleep. Choose models with automatic tip-over shutoff.
  • Close doors to unused rooms and gather in one room to hold heat where you need it.
  • Protect your pipes. Open cabinet doors under sinks on outside walls so warm air can reach the pipes. On very cold nights, letting a faucet drip can also help.
  • Never use a gas oven, grill or generator to heat the home. They can produce dangerous carbon monoxide.

Call One Hour When the Heat Won't Come On

If your furnace still won't turn on after these checks, call One Hour Heating & Air Conditioning® of Delaware, Ohio. We're available 24/7 for heating emergencies, and you can book online 24/7. We're always on time, guaranteed: if we're even one minute late to your appointment, we pay you back. You also get StraightForward Pricing®, a 100% satisfaction guarantee for two years and financing options. We're independently owned and operated in Delaware and serve Delaware, Sunbury, Marysville, Ostrander, Plain City, Johnstown, Alexandria, Raymond and nearby communities.