Bleed an Oil Furnace

If you’ve tried the furnace reset button, checked to make sure there is fuel oil and your furnace still won’t start, don’t fret. Before you call the repairman or start shopping for a new furnace, check the fuel source and make sure the line to the furnace is void of air. Running low on or being out of fuel can cause a furnace to not restart even after you replenish the fuel supply. You may simply need to bleed an oil furnace line and start it up again.



Steps

Prepare to Bleed the Furnace

  1. Turn the furnace off before starting any work on the fuel pump.
  2. Locate the bleed screw on the fuel pump near where the fuel line comes in. The screw is usually a small nipple-like screw.
  3. Place a small bucket or pan under the bleed screw. The bucket will catch any fuel that sputters out as you bleed an oil furnace.
    • If the screw is in an area that is impossible to put a bucket or small tray under, use a flexible tubing just big enough to fit over the bleed screw. Place the tube over the bleed screw and direct it to an area where you can fit the tray or bucket.

Bleed the Furnace

  1. Use a small crescent wrench or pliers to slightly loosen the bleed screw. Make sure the screw remains on the pump and is only a little loose, so it doesn’t fall completely off when you bleed the oil furnace.
  2. Push the reset button on the furnace to turn it back on. As the furnace starts to suck fuel in, air and fuel will spit out of the bleed screw.
    • Keep your pliers or wrench on the screw ready to tighten it. This will also ensure the screw remains in place, if you did loosen it too much.
    • If the furnace cycle ends before the air and fuel mixture stops sputtering, you’ll need to push the reset button again to continue the bleed process until the furnace pushes out all the air from the line.
    • Some furnaces may have a lockout system that won’t allow you to reset more than one or two times. If this happens, you can override the lockout by holding the reset button in until the furnace kicks in again.
  3. Tighten the screw as soon as the air stops sputtering out and a steady stream of fuel pours out. Be careful not to tighten it too much. Replacing a stripped bleed screw can be a very costly project.
  4. Let the furnace continue to run. It should run normally without problems now. If it doesn’t restart the next time, check the line for air again by repeating the bleed process. You may not have gotten all the air out the first time, or you may have a debris blockage in your fuel line.

Things You’ll Need

  • Pliers or wrench
  • Bucket
  • Rubber gloves

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Sources and Citations

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