How to Bleed Baseboards and Radiators - Richard, my wife and I just purchased a new (older) home that has a hot water boiler in the basement. We used it last winter with no problems. We think it makes excellent heat, much better heat than the old forced air system we had in our previous house.

The problem is that some of our radiators have stopped heating. I am wondering what happened. Our boiler works fine, and most of the radiators work. But there are a few that do not heat at all. Please help!! Thanks

Hot Water Heating How to Bleed Radiators

Radiators located on upper floors are especially susceptible to a hydronic airlock

How Does Air Get in the System? How to Bleed Baseboards and Radiators

Have no fear as this problem happens from time to time and most of the time can easily be rectified by yourself with a little basic maintenance. We get this question sometimes. “How to Bleed Baseboards and Radiators?” All hot water boilers need some kind of air management to get rid of air from the system. Additionally, any water introduced to the boiler system will have tiny air bubbles in the water.

These little tiny air bubbles, while separate, are usually no problem. However, from heating and cooling over and over again, these air bubbles combine and make one big air bubble. This air will eventually cause a hydronic airlock.

This means the air in the system builds up to a point where it will cause the water to cease circulating. There are ways to mitigate this and it begins with a good boiler loop design with the proper air management components located in the proper positions in the boiler water loop. That is beyond the scope of this article. However, if you peruse the boiler categories, you will find more information about these components if you are interested in that.

Otherwise, if the problem is very severe, you can call a boiler installation contractor to make changes in the loop to stop or slow the problem.

Bleeding the Air

This problem can occur with baseboards and radiators on a hot water boiler system. In a properly designed system, you should have air bleeders on the radiator or the piping near the baseboard. These air bleeders should be easily accessible, and depending on the type of air bleeder valve will depend on the tool or key need to bleed the air from the radiator or baseboard.

Hopefully, you have a key or a bleeder valve that will require a simple straight-slot screwdriver to bleed. There are some cases where some radiators and baseboards do not have bleeders, and we’ll cover that below. Now, find the bleeder valves on your radiator or baseboard. Furthermore, they should look something like this (with the key for the valve on the left):

Air Bleeder and Key

Baseboard Radiator Bleeder Valve and Key


How to Bleed Baseboards and Radiators with Bleeder Valves

If the system is hot and the boiler has been running be careful not to burn yourself when performing this procedure

That is not difficult, and it should not take much time. I always carry a rag with me to catch any water that may drip or even spray out. If the system is hot and the boiler has been running, be careful not to burn yourself when performing this procedure. Find the air bleeder valve and open it slowly. If water comes out right away, then this radiator or baseboard should be okay. It will require no further bleeding. It is likely if it is one of the radiators or baseboards that were not working that you get some air that bleeds out of the bleeder valve when you first open it.

Of course, you want to open the valve slowly and maybe an eighth of a turn. Eventually, the air will bleed out, and you will get water. That is when you will need the rag to catch the water. When you get all water (no air), then close and secure the bleeder valve and move on to the next radiator or baseboard.

If There are no Bleeder Valves - What to Do? Baseboard Heat Without Bleeders

How to Bleed Baseboards and Radiators

In some cases, either because of poor design or cutting corners, there may be no bleeder valves in your radiators or baseboards. In any case, in the risers within the hot water boiler loop, there should be automatic air vents. Automatic air vents will automatically bleed the air from the system (see photo above). Furthermore, the automatic air bleeders can become fouled and need replacing.

Furthermore, other problems with poor circulation in a hydronic loop or hot water boiler loop can cause issues with heating. Peruse our site here, and you will likely find an article addressing these issues. Here is a photo (an older photo with not so great quality) of boiler installation. The piping arrangement should have valves and drains for a fast purge of the entire loop system.

Near boiler piping air purge

The boiler drains, and the gate valve installation in such a way as to allow a full purge. A full purge of the entire loop using the make-up water or a water hose. The pressure reducer valve has a fast-fill handle on it to override the pressure reducer. Use the override, if equipped, to give it full pressure as supplied by the city or well system.

If you ever do this way of purging air make sure to allow the boiler a cool-down period to prevent thermal shock. Furthermore, that is if your boiler has such a piping arrangement on it. Many do not because the installers cut corners or do not know how to install a boiler loop system.


How to Make Baseboards and Radiators Hotter by Bleeding Air

As may see, not all boiler systems are the same. These are not out-of-the-box systems where one size fits all. Many loops installations happen by either a plumbing company or an HVAC company that specializes in boiler systems. Piping arrangements are different from installation to installation. Furthermore, some installations cut corners on various components and valves. Furthermore, this often leads to serious problems later on down the line.

I’ve witnessed installations after the fact where someone who did not know what they were doing installed the loop and boiler system. In the long run, it pays to do it right the first time. Finally, it will lead to longer boiler life with the least problems and frustration for all concerns.

High Performance HVAC Heating & cooling

How to Bleed Baseboards and Radiators

Removing Air from Baseboards Video