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Home Notes from the crew

Why a furnace starts and then shuts off

The short answer

Usually a dirty flame sensor or a clogged filter.

A furnace that starts, runs a minute and shuts off is usually telling you one of two things.

Check the filter first

A clogged filter overheats the furnace and it shuts itself off to protect itself.

Then the flame sensor

  • It is a small rod near the burner.
  • Dirt on it makes the furnace think the flame went out.

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