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By Best of Indianapolis Editors Home & Repair

Furnace Won’t Turn On? 6 Things to Check Before You Call for Repair

Homeowner checking the air filter on a basement furnace
Short answer

Check the thermostat, the breaker and furnace switch, the air filter, the furnace door panel, the condensate drain and the outdoor vent pipes. If you smell gas, leave the house first and call 911 or your gas utility from outside.

A furnace that quits on the first cold night of the season is a classic Indianapolis November. Before you book a service call, a few simple checks fix a surprising number of “dead” furnaces.

Safety first

If you smell gas (a rotten-egg smell), don’t flip switches or try to restart anything. Get everyone out, then call 911 or your gas utility from outside. In Indianapolis that’s usually Citizens Energy Group. If a carbon monoxide alarm goes off, leave the house and call 911.

The 6 checks

  1. Thermostat. Make sure it’s set to Heat, set a few degrees above room temperature, and has fresh batteries if it uses them.
  2. Power. Check the breaker for the furnace, and the furnace service switch (it looks like a light switch, usually on or near the furnace). It gets flipped off by accident more than you’d think.
  3. Air filter. A clogged filter can make the furnace overheat and shut itself off. Replace it if it’s gray and dusty.
  4. Door panel. Most furnaces have a safety switch that won’t let them run if the front panel isn’t seated all the way.
  5. Condensate drain. High-efficiency furnaces drain water through a small line or pump. If it’s clogged or the pump is full, a float switch can shut the furnace down.
  6. Outdoor vent pipes. High-efficiency furnaces vent through white plastic pipes on an outside wall or the roof. Snow, ice, leaves or a nest can block them.

Many furnaces also have a small status light that blinks a code. Write the pattern down. It helps the technician even if you can’t read it yourself.

When to call a pro

  • It still won’t start after these checks
  • It starts and shuts off over and over (short cycling)
  • You hear banging or screeching, or smell burning that doesn’t fade after the first run of the season
  • The igniter or flame sensor seems to be the problem

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