how to bleed baseboard radiators - corner baseboard radiator

How to Bleed Baseboard Radiators (With or Without a Key!)

You might need to learn how to bleed baseboard radiators if you find your home getting colder but your temperature is set where it should be.

You may have noticed that your baseboard radiators don’t generate as much heat as they used to. The most likely fix is a DIY project anyone can handle. Here’s how to do it quickly, even if you don’t have a valve key.

How Does a Baseboard Radiator Work?

The concept is fairly simple. Water is heated by a boiler (or another heating source) and delivered to the baseboard’s water supply pipes throughout your home. In electric baseboard radiators, there is no need for a boiler.

Inside the baseboards are coils. The water flows through the coils which heat the metal fins. The hot air is then released through the top of the baseboards and rises into the room.

At the same time, cool air is flowing into the bottom of the baseboard (near the floor) and gets heated. This also lowers the temperature of water in the pipes. The cooled water returns to the heating system to get reheated and recirculated. It’s a continuous loop.

diagram of baseboard radiator
Water flows through the pipe. The fins transfer the heat out the top of the baseboard while cool air goes in, cooling the water in the pipe. The process is a continuous loop, with cooled water recirculating through the heating source to get hot again and get delivered to the baseboard radiator.

Why Do I Need to Bleed My Radiators?

Learning how to bleed radiators is a fairly common maintenance task if you have baseboard radiators. Why?

Over time, air builds up in the supply pipes that provide hot water to your radiator. This prevents heated water from flowing up into the unit. The cure is to remove the air through a bleeder valve. This process is known as bleeding a radiator.

woman in blanket on couch
Brrr. It’s getting cold in here. Time to bleed your baseboard radiators.

How Do I Know if I Need to Bleed My Radiators?

Here’s a quick way to determine if your radiator is working correctly.

  • Turn on the heat and wait until the baseboard radiator is warmed up.
  • Touch the bottom of the radiator. It should be hot.
  • Now move your fingers up toward the top of the radiator. If it gets cooler as you go up, then you should bleed the radiator by opening the bleeder valve plug. The problem is likely air trapped in the pipes that needs to be released.
how to bleed baseboard radiators - feel bottom to top to sense heat
Run your fingers from the bottom to the top of the radiator. If it’s cooler on top, then you have a problem.

How to Bleed Baseboard Radiators (With a Key)

  1. Turn the thermostat up and make sure the water heating system is turned on. Baseboard heating systems can have separate heat zones. Each zone has its own thermostat and zone valve.
  2. Wait until at least one baseboard radiator gets warm.
  3. Trace the supply lines for each heating zone in the hose back to the furnace. Make sure any manual valves in the loop are open.
  4. Check each baseboard radiator, but begin in the room furthest away from your water heater and work your way to the baseboard radiator that’s closest to the water heater. Note any units that remain cold or make loud gurgling or banging sounds (this is from the trapped air which is causing your problem). Just keep in mind that it is normal for them to make other kinds of sounds, like creaking and pinging, as they warm up.
  5. On each of the problem units, turn the inlet valve fully counterclockwise to make sure the unit is open (so water flows). Use a handle, knob or screw to do this.
  6. Hold a cup next to the bleed valve (there may be just one bleeder valve for all the baseboards in a single room). Use the square socket valve key (or bleeder key) that came with your baseboard radiator heating system to open (turn counterclockwise) the bleeder valve until a stead stream of air and water flows out. You can also purchase a key at most hardware stores. Once the air stops coming out, you can close it (turn the key clockwise).
  7. The unit shouldn’t take longer than 5-10 minutes to start heating up. If the unit is still cold after 10 minutes, contact a plumber or heating professional.
how to bleed baseboard radiators without a key
If you have a key to the bleeder valve, the process is super simple. Just insert the key, turn counterclockwise to open, and let air and liquid out until all the air has been released. Don’t worry about the water, it’s the air we’re concerned with.

How to Bleed Baseboard Radiators (Without a Key)

In this process, only one step has changed. Pay particular attention to Step #6 if you don’t have your radiator key.

  1. First, make sure the water heating system is turned on. Baseboard heating systems can have separate heat zones. Each zone has its own thermostat and zone valve.
  2. Wait until at least one baseboard radiator gets warm.
  3. Trace the supply lines for each heating zone in the hose back to the furnace. Make sure any manual valves in the loop are open.
  4. Check each baseboard radiator, but begin in the room furthest away from your water heater and work your way to the baseboard radiator that’s closest to the water heater. Note any units that remain cold or make loud gurgling or banging sounds (this is from the trapped air which is causing your problem). Just keep in mind that it is normal for them to make other kinds of sounds, like creaking and pinging, as they warm up.
  5. On each of the problem units, turn the inlet valve fully counterclockwise to make sure the unit is open (so water flows). Use a handle, knob, or screw to do this.
  6. Hold a cup next to the bleed valve (there may be just one bleeder valve for all the baseboards in a single room). If you don’t have a socket valve key, use either a screwdriver, needle-nose pliers, hex wrench, or socket wrench (whichever is appropriate for your type of valve) to open the valve until a steady stream of air and water flows out. Once the air stops coming out, you can close it.
  7. The unit shouldn’t take longer than 5-10 minutes to start heating up. If the unit is still cold after 10 minutes, contact a plumber or heating professional.
how to bleed baseboard radiators with a key
If you don’t have a key, you’ll need to determine which kind of bleed valve you have. Some can be opened with a screwdriver. Some need to be opened with needle-nose pliers, a hex wrench, or a socket wrench. In all of these cases, you’ll open in a counterclockwise direction and close in a clockwise direction.

Final Thoughts

If you don’t bleed your radiators routinely, air collects in the pipes and prevents hot water from getting to your baseboard radiator. You’ll end up with a slowly but surely colder house.

Take time every now and then to observe if your room is getting colder even if you have the temperature set where you want it. Or if you hear gurgling or banging sounds coming from them.

If so, perform the hand-test described above on your baseboard radiators. If it fails your test, go ahead and bleed them as shown above. And to be safe, bleed your radiators at least once annually.

Call 1-Tom-Plumber

Don’t hesitate to contact us here or call us at 1-Tom-Plumber (1-866-758-6237) if you need help with the plumbing on your radiator heating system.

1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing, drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.

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