How to Purge Air from a Hot Water Boiler

Man working on a boiler
  • 1 hours
  • Intermediate
  • 0-20
What You'll Need

Every so often, your hot water boiler will need to have air purged from it. An indicator that it’s time is when it’s not providing sufficient hot water. Basically, purging your boiler will involve getting all of the air out of it so the water that is in the boiler will be able to run through it freely. Any air bubbles trapped inside of your boiler will only end up stopping the water flow, and will cause your boiler to need to be purged so it can function properly.

Step 1 - Initiate Water Feed Valve

Firstly, turn on the main water feed valve. Whenever you do this you will be letting the water flow straight into your boiler.

Step 2 - Clean Out Air

Once you have the water feed valve fed into your boiler you will be ready to get the air cleaned out of it. Either right at the top or towards the top of your boiler you will be able to see either a wrench adjusted nut or a spring loaded pressure valve. Whatever is up there and its exact location will depend heavily on the type of boiler you have and its age. If it is a spring loaded valve you will be able to use your fingers to open it. If it happens to have a nut, then get out your wrench to loosen it. There is going to be a hissing sound as you open up the valve. This is normal as you will be purging the air from the boiler.

Step 3 - Position Bucket

boiler in a garage space

Now position your bucket well underneath your valve. It is important you have all of your necessary tools handy before you begin this next step. The bucket needs to be in position and ready as soon as you begin to purge your boiler as you do not know exactly when the water will start coming out. As soon as the hissing stops the water is going to start coming out of your valve. The bucket will allow you to catch the water without flooding the area. Make sure that as the bucket is catching the water, you are working on stopping the water flow. You will either do this by releasing your spring loaded valve with your fingers or by using your wrench. As soon as you have gotten the water turned off your boiler is going to be free of all air.

Step 4 - Water Supply

Once you have gotten your water turned off to the boiler and your boiler air-free, dump the water out of your bucket and clean up any excess spillage with your rags.