Take a few hours to properly inspect, flush, and refill your boiler to address problems with trapped air. A professional will be much speedier, but learning boiler maintenance can be helpful for homeowners.
Cost
$25–$50
DIY with what you have.
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What you'll need:
TOOLS
Standard garden hose
Bucket
Towels
Work gloves
Wrench
In some hydronic (water-based) baseboard heaters, air can seep into the pipes over time. That can cause loud noises, a drop in heating efficiency, and boiler problems if left unattended. Standard hydronic baseboard heaters have a built-in solution called bleed valves, which users can open to bleed out excess air and fix related problems. But if you can’t find the bleed valves, here’s how to bleed a baseboard heater without a bleed valve.
Prepping to Bleed a Baseboard Heater
Before you assume your home baseboard heating system doesn’t have bleed valves, it’s worth double-checking by looking up your heater or boiler model. Your boiler or heater model number should be on a plate connected to the boiler or other key components. Look up the model number online and see if you can find a manual showing how it works. This will help you locate and use any bleed valves.
In many cases, the bleed valves are simply hidden under baseboard heater covers or side panels, and the manual can help you locate them. Sometimes, the boiler uses a central bleed valve instead of separate valves for each heater, or it uses a specialized vent to automatically remove air bubbles from the system so you don’t have to bleed the system at all during normal operation. It's uncommon for a hydronic baseboard heating system to have no way of removing trapped air at all, which is why it’s important to find a manual and check the details. But if there really are no bleeding or air venting options, you can proceed with the steps below.
How to Bleed a Baseboard Heater Without a Bleed Valve
Bleeding a baseboard heater without a bleed valve involves turning off the boiler, checking the zone valves, attaching a hose to the drain or purge valve on your boiler, opening the drain valve to drain water out of the affected zones, and simultaneously using the fill valve or feed valve to add new water to the system until the water runs smooth without any air bubbles. Our step-by-step instructions will walk you through the entire process.
Shut down the boiler completely and wait for it to cool down. You don’t usually have to switch power off to the boiler room entirely, but it’s a potential safety step if you’re worried about any risks.
Check Your Zone Valves for Blockages
In a hydronic baseboard heating system, pipes from the boiler lead to each baseboard heater or zone in the house. Sometimes it’s very easy to tell which pipes lead to which zones, and sometimes the boiler design makes this difficult. Study your boiler and find the pipes leading to the zones that are having problems or making strange noises.
Once you find the pipes, check their valves for normal operation. Make sure the valves to the zones are wide open. In some cases, problems similar to trapped air occur if the valves have failed or are only partly open. This can be fixed by moving them to the proper position.
Find the Drain or Purge Valve on Your Boiler
Look for the drain or purge valve on your boiler, which is how you can drain the boiler tank’s water supply (again, the manual comes in handy here). It should be on the boiler, close to the bottom of the tank.
Close the Zone Connections You Don’t Want to Bleed
Close the valves to all the zones that are functioning normally, leaving only the zones experiencing problems open. Make sure the zone connections are shut tight so no air enters them during this process.
Connect the Hose to the Drain Valve and a Bucket
Before opening the boiler drain valve, connect your hose tightly to one end and place the other end in a five-gallon bucket. You want all the boiler water to drain out into the bucket. Since you’ll be draining a significant amount of water, have plans to empty the bucket as you work, or drain out through a door or window into another drainage spot instead.
Open the drain valve and begin draining out the water in the boiler and the affected zones. Note this is not the same thing as a full purge, since you’re only draining the affected heater(s), and you don’t want the boiler to empty entirely. Optional: This is a good time to check for sediment lingering in your boiler, which could be causing additional problems.
Use the Fill Valve or Feed Connection to Fill the Boiler As It Drains
Your boiler should have a fill valve or a feed valve to add more water to the system. Set that valve to open or to fill mode and add new water to the boiler system as the old water drains. Continue this cycle until the water runs smooth and clear without any air bubbles. Then switch the feed valve off the fill setting and close the drain valve.
Open the Zone Valves Again and Test Boiler Operation
Open the valves to all the zones you had blocked off before, and turn the boiler back on. Let it heat up, and check the heaters that were giving you problems to see if their issues have been resolved.
DIY vs. Hiring a Pro
Don’t hesitate to hire a local baseboard installation pro for this project if necessary, especially if you don’t know your own boiler very well. An HVAC or heating professional can double-check that your bleed valves aren’t hiding somewhere and arrange an air bleed that works without damaging your system. They may also suggest a full purge to fix sediment issues or air problems.
General HVAC maintenance costs are around $250 for a visit and can include checkups as well as quick tasks like bleeding out air. Basic baseboard heater repairs can cost between $140 and $440 on average.
Frequently Asked Questions
If you want to switch to baseboard heaters that have easy-access bleed valves, expect to pay between $300 to $500 per heater, labor included. Keep in mind that a large heater replacement may require a boiler replacement, too. Get quotes and advice from experts in your area as you’re making your plans and setting a budget.
In general, it’s a good idea to bleed air from your heaters at the start of every cold season, before you move your boiler system back into active mode. Early fall is a common time for this task. However, some heating systems don’t need much manual bleeding because of automatic bleed vents and other components.
Once you know where your bleed valves are and how to use them, bleeding out heaters is a quick process. Expect it to take around 10 to 20 minutes, possibly longer if you have a lot of heaters or are still learning how they work. If you have a central bleed valve on your boiler, the process still takes the same amount of time. Make sure you have any keys necessary to turn the bleed valves on. Without bleed valves, the process should take around three hours.
Not every type of baseboard heater needs to be bled. Hydronic baseboard heaters need to have air removed at least occasionally, but electric or gas versions that don’t use water at all don’t need to be bled. There are no pipes or valves on these models to worry about, nor any central boiler. Instead, they use heating elements or other methods to supply direct heat to a room.
Tyler Lacoma has spent more than 10 years testing home technology and the latest tools to help keep readers current for their next project. His published work can be found on Family Handyman, U.S. News & World Report, and Digital Trends.
Tyler Lacoma has spent more than 10 years testing home technology and the latest tools to help keep readers current for their next project. His published work can be found on Family Handyman, U.S. News & World Report, and Digital Trends.
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