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Furnace Stopped Working?

Four Things to Try

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modulating furnace

Modulating Furnace

© Lee Wallender; licensed to About.com
I came home late one night and found the temperature in my house hovering around 58 degrees F and rapidly getting colder. The modulating furnace wasn't running. Earlier in the day, I had been working on a joist near the furnace. As such, I turned off the furnace at the thermostat. It wasn't absolutely necessary, since I wasn't working on the furnace itself, but I didn't like having a hot furnace near me.

With the furnace not working, I looked at:

  1. Circuit Breakers: I went downstairs and looked at the circuit breakers to see if they were flipped off. Your furnace may have two circuit breakers, not one. They should be next to each other, top and bottom. Or it may have a single, jumbo-sized breaker.
  2. Furnace Pressure Switch: Our Home Repair Guide mentions that the furnace pressure switch may shut down the furnace automatically if "abnormal conditions" are present, such as air leaks, clogging, restricted air intake vent, etc.
  3. Fan: My furnace has a toggle switch on the side that allows me to manually turn on fan-only operations. Flipping this switch and listening for the fan turning on is a way to double-check that the furnace is receiving power. It verifies that, even if the burner part of the furnace isn't operable, other parts are working.
  4. Thermostat: Is the thermostat properly triggering the furnace? It's one of those solutions that seems all too simple. But sometimes a child, guest, or even you may interfere with the workings of your thermostat.
Read: Troubleshooting Your Electric Ignition Furnace

My solution is a testament to how it's necessary to keep your mind open to all possibilities. It's also an illustration of dumb home remodeling maneuvers.

After I opened up the panel to the furnace and looked in, I saw the circuit ignition control system, let out a gasp, and decided to call the HVAC company first thing in the morning.

Then I saw a cloth-covered wire at least 50 years old leading into the furnace. Since this was nearly a brand-new furnace, the wire looked out of place.

Then I remembered earlier in the day, working on the joist, I snipped an old internal telephone wire to get it out of the way. Or so I thought.

As it turns out, the old Bell phone wire was really the wire leading from the thermostat to the furnace. Snipping this old landline wire was so inconsequential that I had forgotten about it right after doing it.

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