If your Furnaces suddenly stops heating in winter, don't rush to call a technician. Check these 8 items in order—many problems can be fixed in minutes, saving a service call.

If you smell gas (like rotten eggs): do not turn lights on/off, do not use the phone; leave the house immediately and call the gas emergency number or 911 from outside.

1. Thermostat settings

  • Is the mode set to “Heat” (heating) instead of “Cool” or “Off”?
  • Is the set temperature a few degrees higher than the current room temperature?
  • If the thermostat screen is blank, replace the battery first.
  • Check if the smart thermostat (Nest, ecobee, etc.) is set to “Leaving home” mode or has a schedule lowering the temperature.

2. Furnaces power switch

There is usually a switch on the wall next to Furnaces that looks like a light switch, and it’s common for someone to accidentally turn it off when passing by. Make sure it’s turned on.

3. Circuit breaker

Check your breaker panel to see if the circuit for Furnaces has tripped. You can reset it once; if it trips again, don’t keep resetting it—call a technician.

4. Furnaces door panel

If the door panel in front of Furnaces isn’t installed properly or fully closed, the safety switch will prevent Furnaces from starting. This is the most common problem after changing the filter.

5. Filter

A dirty filter can cause Furnaces to overheat and shut down automatically for protection.

  1. Turn off the Furnaces power switch.
  2. Remove the old filter (usually located on the Furnaces side or below the return air duct).
  3. Check the size on the edge of the old filter and install a new filter of the same size. Arrow points to Furnaces.。
  4. Turn on the power.

6. Outdoor intake and exhaust pipes

High-efficiency Furnaces has two white plastic pipes on the exterior wall. Heavy snow or ice can block pipe openings, causing Furnaces to shut down due to poor exhaust. Clear snow and ice carefully from pipe openings, wait a few minutes for it to restart (be careful not to damage the pipes).

7. Condensate drain pipe and pump

A high-efficiency Furnaces produces condensate water, which drains through a small plastic pipe into a floor drain or a small pump. If the pipe is blocked or the pump is faulty, water can’t drain and Furnaces will shut down. Check around Furnaces for water buildup or if the pump is full.

8. Check the fault indicator light

Many Furnaces have a small window with a blinking indicator light. Count the flashes, check the fault code chart on the back of the door panel, and tell the technician when you call to help them diagnose the problem faster.

Call a technician for these issues

  • If all the above are checked and it still doesn’t heat
  • You can hear the ignition sound but it goes out quickly (commonly caused by a dirty flame sensor that needs professional cleaning).
  • Furnaces making unusual noise or burning smell
  • If the carbon monoxide alarm sounds: open windows immediately, leave the house, call 911.
  • If your Furnaces is over 15–20 years old and breaks down often, you might consider replacing it

See repair pricing. Furnace / AC Repair cost, Replacement recommended Furnace Replacement cost. Perform annual maintenance before winter to avoid most sudden breakdowns in winter. Furnaces maintenance cost。

FAQ

Why does Furnaces keep starting and stopping repeatedly?

Common causes are dirty filter causing overheating, dirty flame sensor, or thermostat placed in a poor location (e.g., near a warm air outlet). Replace the filter first; if it doesn’t help, call a technician.

Furnaces is blowing cool air.

It's normal for it to blow cool air briefly after starting. If it keeps blowing cool air, the ignition may have failed (issues with gas valve, igniter or flame sensor) or heating stopped due to overheating or blocked exhaust. Follow the steps above to check.

What to do if your heater breaks down in the middle of the night and you can’t wait for a technician?

Use an electric heater (keep away from curtains and furniture, no extension cords), close doors to unused rooms, and open cabinet doors on exterior walls to prevent pipes from freezing. Never use gas stoves or BBQ indoors for heating due to carbon monoxide poisoning risk.