Tips & Tricks

How to Bleed a Furnace?

If your home’s furnace isn’t working properly there are several typical steps you’d want to try before calling a technician – resetting the ignition button, refilling the oil, and checking if the thermostat is working properly. There is one last thing you’d want to try before calling a professional – bleeding the furnace.

How do you bleed a furnace, however? Here are the 7 main steps:

  1. Turn the furnace off. Before you start bleeding a furnace’s fuel pump you should always turn it off. How you do this will depend on the model but typically you’ll need to flip the pump’s switch or turn it off directly at the breaker. You’ll also want to turn the gas off at the shut-off valve at the gas line.
  2. Find the bleed screw. Again, its exact location will depend on the model but it should be near the entrance of the fuel line into the pump and it should be pointing downwards.
  3. Place a small bucket or another vessel below the bleed screw before unscrewing it. You’ll bleed the furnace into the bucket. If you can’t fit a whole bucket under the screw try something smaller like a pan or use a tube to direct the “bleeding” to a bucket on the side.
  4. Unscrew the bleed screw. You can use a standard crescent wrench or pliers to do this, whatever you have on hand.
  5. Turn the furnace back on by pushing the reset button. Bleeding oil furnace works the same way as bleeding a propane furnace – the fuel will start sputtering with air through the bleed screw as the furnace starts sucking it. Leave the fuel sputtering for as long as there’s air coming out with it. Once air stops “bleeding” and all you have is fuel flowing evenly, grab the wrench again.
  6. Tighten the bleed screw again. Be careful not to tighten it too much or damage it in the process – replacing a damaged bleed screw is surprisingly costly.
  7. You’re done – leave the furnace running if you want to. Know you know how to bleed oil furnace and you can do it whenever you need to in the future!

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