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Baseboard Heating

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Baseboard Heating Draining System

The Home Wizard app calculates your ideal home care program to avoid problems with your Baseboard Heating, but sometimes trouble can still occur. Here are answers to questions about baseboard heating draining system.

QUESTION FROM mjones61380

My husband and I like to fix things ourselves. We bought a new circulator for our fuel fired baseboard furnace. We know that we need to drain our system and shut off the water source but are unsure how to do this. We also will have to put water back in and get rid of air. Can you walk us through this or send us in the right direction? A how to guide? Electric portable heaters are fine for a little while but it sure is cold at our house!



Dear mjones61380:

Regarding a procedure draining, re-filling and purging air from your baseboard heating system, it will depend on your specific configuration of valves, etc. But in general, here is the procedure a baseboard heating system:


1) locate the main supply valve and back-flow preventer valve for your hot water baseboard system. Your back-flow preventer valve prevents water from your heating system from flowing backward into your household supply, and it typically looks something like the one pictured here with a release lever on top:

2) turn off your boiler and heating system, and turn all of your thermostats down to their lowest settings. It sounded like your system is currently turned off, but just so you know, I normally suggest letting the heating system cool down before purging the air out of the system. There are two reasons for this: 1) as the water cools down, dissolved air in it will be released from the water, which will then allow you to purge this air out as well; and 2) less risk of being scaled by hot water. However, if it is not practical for you to let your system cool completely down, then you can still drain, re-fill and purge the system, but just be careful of the hot water. But again, this doesn't sound like it applies to you, if you system has been turned off for a while.

3) make a note of which valves are open, and which are closed.

4) if your piping allows it, close the valves that allow you to isolate your boiler from the rest of the system (so that you don't get a pressure spike that causes your boiler's pressure relief valve to lift, as this weakens it).

5) connect a drain hose to safely drain hot water from your system to a floor drain, or to outside. Be CAREFUL, as the water coming out can be scalding HOT.

6) close the main supply valve to your hot water system.

7) one-by-one, open the valves for each zone of your system that allows the zone to flow out of the main drain valve for your system. After each zone has been drained, close its drain valve.


1) follow your pipes around starting with your backflow-preventer valve, and then for each zone one-by-one open only those valves necessary to allow the fresh water that is coming into the system from the backflow-preventer valve to flow through the particular loop that you are trying to re-fill and purge (that is, one loop at a time), and then to flow out the drain hose that you have connected. If you look at your back-flow preventer valve, the small lever on the top of the valve operates the bypass for the pressure reducer for the valve. So as you lift up on the lever, it opens the valve to street pressure from your water supply. So as you start to re-fill and purge the air from one of your heating system loops, you can lift the lever to increase the pressure to get stronger flow to the line that you are trying to purge. But let the lever down if the pressure in your system starts to go too high (however, if you isolate you boiler properly, as described below, then you won't have to worry about over-pressuring your system). Close the drain valve for each zone's loop as your finish re-filling and purging the air out of it.

2) close the main drain valve and disconnect the drain hose.

3) return all of your valves to their original operating position (especially the valves that you used to isolate your boiler).

5) check to see that you have re-opened your heating system's main supply valve.

6) turn your boiler and heating system back on.

7) check the pressure gauge on your system, and inspect for any leaks around valves that you have opened or closed.

8) put your thermostats back to their desired settings.

Since you have isolated your boiler from the re-filling and purging process, this procedure will not purge air from this segment of your system. But this is a relatively small area compared to your entire system, and the benefit to isolating it, is that you don't need to worry about over-pressuring your boiler while you are doing the air purging.

Also, here are is an additional suggestion that you might find helpful. If you haven't had your annual inspection done yet on your boiler, then when the service technician comes out to do your inspection and service, you can ask them to show you exactly how to drain, re-fill and purge your specific system, when they can be physically there to point out what each of your valves does exactly what, for your particular system.

Hope this is helpful.


I am building new walls in my basement and the pipes from my hot water baseboard pipes are coming straight down and i need to put an elbow on the pipe how do i drain and refill and purge the hot water system.

thank you.


Dear Bill:

Regarding your question of how to drain and refill and purge the hotwater system for your baseboard heating system, first, to drain your system, shut off your boiler and make a note of the water pressure. Next locate the self-feeding (auto-makeup) water valve and ensure that your make-up water supply is shutoff. Next, attach a garden hose to one of the spigots coming off of the return line that goes back to your boiler, and run the other end of the hose to either a drain or to outside. Then open up all of you valves that go to your various heating zones. Then open up the spigot and let the water drain out through the garden hose. If your boiler has been running, then BE CAREFUL that the water can be scalding hot.

To refill and purge the air from your system, ensure that the make-up water supply is connected and water supply valve is open. Close them all, and then one at a time, open the valve to each heating zone of your house. Then while manually opening the auto-makeup valve, keep the spigot open and let the water run out the garden hose to your drain our outside. Let it run until you no longer see any air bubbles. While you are doing this, keep an eye on the water pressure and don't let it get above 25 PSI. If needed to control the pressure, release the auto-makeup valve momentarily. After you have stopped seeing air bubbles, release the auto makeup valve and close spigot. Allow the water pressure to return to normal. You then repeat these steps until all of your zones have been bled. When done, put your zone valve to their operating positions. Then check the water pressure, which should be the same as what you noted at the beginning. And then finally, turn your boiler back on.

Hope this is helpful.


I want to disconnect my existing cast iron boiler in order to move it 12 inches or so and then reconnect. I have baseboard style heaters but they appear not to have bleeder valves on them in order to drain the system down. What would be the best way to ensure the entire system is drained down. I also have a system when installed that has no shut-off or service valves to isolate the piping to the baseboard heaters , only the boiler drain at the floor level and a boiler drain right where the piping attaches to the supply side. Any ideas would be appreciated.


Dear Jesse:

Actually, baseboard heating systems do not usually have bleeders on the baseboard heating pipes. But at your boiler, there should be purge valves. So after you shut off your boiler and you close your water supply valve, you should be able to drain your system by opening up the other valves around your boiler.

Hope this is helpful.


I am going to renovate my bathroom and I need to move two hot water heaters. I have two pumps. One for upstairs and one for downstairs. Can I drain the upstairs zone with out draining the downstairs? One other thing when I want to heat the basement and not the upstairs. The upstairs heats too. I didn't have the upstairs pump on. My boiler is oil and my house was built in 1963 and pipes are copper.


Dear Mark:

Regarding whether you can drain one zone without affecting the other zone, it will depend how your particular system is piped. However, since you said that when you run only the basement zone that the upstairs heats up too, then I would suspect that the two zones are connected somewhere (for example, they may share a common return section).

Hope this is helpful.

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