Introduction: How to Bleed a Hot Water Heating System


It's winter and comes with it heating issues. One common issue is air in a hot water heating system. I will explain how I was able to fix and bleed my hydronic hot water boiler system in this Instructable.

How can you tell if you need to bleed your hydronic heating system?

There are a few signs:

  • you can hear gurgling or other odd sounds coming from the radiator or plumbing
  • a sound like draining water coming from the heating pipes
  • inadequate heating, the radiator or baseboard isn't heating up

If you have more than one zone in your house for heating you may need to bleed each one separately.

Step 1: Video

I explain how I bleed my hot water system in this video but I will explain in the following steps as well.

Step 2: Radiator or Hot Water Baseboard

In North America there are mainly two types of hot water boiler heating, radiator or hot water baseboard. There is also in floor heating but I'm not as familiar with that so I can't comment on it directly.

To bleed air from a radiator, there will be a butterfly looking screw that can be loosened to let built up air out.

A baseboard heater looks like an electric baseboard heater except of having a electric heating element, there is plumbing for a copper pipe and aluminum fins. This is what I will I will concentrate on from here.

If for some reason air gets into the system and you need to bleed it you will need to find the bleeder screws. The bleeder screws usually will be located on one of the baseboard heaters if they were plumbed correctly. If it was not like my system you will need to have them installed.

There are two types of bleeders, a manual one or a automatic one. The bleeder ideally should be located at the highest point of the heating system as that is where the air will accumulate.

To see what the two types look like see the pictures.

Step 3: Automatic Bleeder Vs Manual

The automatic bleeder does exactly what it sounds like it will do, it will passively bleed the heating system of air. If there is a lot of air in the system it will take some time but eventually it will remove all the air. They do fail so keep an eye on them and change them every few years.

The manual bleed is much less complicated but requires you to go bleed off the air by turning the valve and letting the air escape until water comes out.

If you are going to the trouble of installing bleeders I would recommend the automatic bleeder. You will need to solder in elbows on the baseboard heater. But if you don't have access or don't want to go to the trouble of installing them on the baseboards above where the boiler is, you can also installed them inline somewhere. It's not ideal but if the air can circulate through the system, it will over time will eventually end up at the automatic bleeder if it was installed inline as there is just enough room in them to accumulate the air.

If you install a manual one it will have to be at the highest point as constantly checking to let air out is not ideal if it was install inline and at a point that is lower than the rest of the heating system.

I hope this helps you out on how to bleed your heating system.