How to Bleed Air from a Boiler

Have you ever noticed parts of your building aren’t heating as they should, or perhaps strange noises coming from your radiators? These issues can often be traced back to a simple yet frequently overlooked problem: trapped air in the boiler system. Air in the system reduces heating efficiency, causes inconsistent temperatures, and can even lead to higher energy costs. Left unresolved, it can create more significant and expensive problems down the line.

This guide will explain how to bleed a boiler and why it’s crucial to maintaining a healthy, efficient heating system. With a few simple steps, you can prevent heating inefficiencies, avoid unnecessary downtime, and keep everything running smoothly.

Why Air in Your Boiler System Is a Problem

Air in a boiler system can affect how well the system heats your property. Boilers circulate hot water or steam through radiators, pipes, and coils to provide heat. When air enters this system, it disrupts the flow of water and reduces the heat transfer. You may notice that certain radiators aren’t getting warm or that parts of your building are inconsistently heated. Over time, this can cause discomfort and increase your energy bills, as the boiler has to work harder to maintain the desired temperature.

Another issue is the potential for corrosion. Air in a closed system like a boiler contains oxygen, and when that oxygen comes into contact with the metal components of your system, it can lead to rust and eventual leaks. By regularly bleeding air from the system, you can mitigate these risks and prolong the life of your boiler.

Signs That Air Is Trapped in Your Boiler System

Before you grab your tools and start bleeding your boiler, you need to know whether air is actually trapped in the system. Here are a few telltale signs that air might be causing problems:

1. Cold Spots on Radiators: If some parts of a radiator feel warm while others are cold, this uneven heating is a sign of trapped air. The warm water cannot circulate fully, so heat doesn't reach all areas of the radiator.
2. Strange Noises: If you hear gurgling, banging, or whistling sounds coming from your boiler or radiators, it’s often an indication that air is trapped in the system. This air interferes with the natural flow of water and creates pressure imbalances.
3. Reduced Heating Efficiency: If you notice that your property is taking longer to heat up or that certain rooms remain cooler than others, it may be due to air pockets restricting the flow of hot water.
4. High Pressure Readings: Air can cause pressure to fluctuate in the boiler. If you notice that the pressure gauge is unusually high, it may be due to excess air trapped in the system.

Tools You'll Need to Bleed Your Boiler

Bleeding air from a boiler is a relatively simple task that doesn’t require a lot of specialized equipment. However, having the right tools on hand will make the process smoother and help you avoid damaging your system. Here’s what you’ll need:

1. Radiator Bleed Key: This is a small tool that fits into the bleed valve on your radiators. Most modern radiators have a square or slotted bleed valve, and this key is essential for opening the valve.
2. Flathead Screwdriver: Some radiators, particularly older ones, have a bleed valve that can be opened with a flathead screwdriver instead of a bleed key.
3. Towels or a Container: When you open the bleed valve, water may drip out along with the air. To catch any excess water and protect your flooring, it’s a good idea to have towels or a container ready.
4. Gloves: Boiler systems can get very hot, so it’s smart to wear gloves to protect your hands during the process.

How to Bleed Air From Your Boiler: Step-by-Step

Now that you know why bleeding air is essential and have gathered your tools, it’s time to get started. Follow these steps carefully to bleed the air from your boiler system safely and effectively.

1. Turn Off the Boiler

Before you do anything, make sure to turn off the boiler and let the system cool down. Working with a hot boiler can be dangerous, as hot water and steam can escape when you open the bleed valves. Give the system enough time to cool off completely to avoid burns or other injuries.

2. Locate the Radiators

Once the boiler has cooled down, go to the radiators. You’ll need to bleed each radiator individually, starting with the one furthest away from the boiler. Air tends to accumulate in the highest or furthest points in the system, so working from the farthest point ensures you’re clearing the air as you go along.

3. Open the Bleed Valve

Using your radiator bleed key or a flathead screwdriver, locate the bleed valve at the top corner of the radiator. Place a towel or container underneath the valve to catch any water that may come out. Slowly turn the key or screwdriver counterclockwise to open the valve. You’ll hear a hissing sound as air escapes. This is precisely what you want.

4. Wait for Water to Drip

Once the air has escaped, water will begin to leak out of the valve. When you see water dripping steadily, it means all the air has been bled from that radiator. Close the valve by turning the key or screwdriver clockwise until it’s snug but not overly tight.

5. Repeat for Each Radiator

Move to the next radiator and repeat the process, working your way back towards the boiler. Remember to start with the radiator furthest from the boiler and work towards the closest one. This ensures you are pushing the air out in an organized manner.

6. Check Boiler Pressure

After you’ve bled all the radiators, it’s important to check the pressure gauge on your boiler. Bleeding the system will cause the pressure to drop slightly. Ideally, your pressure should be between 1.0 and 1.5 bar. If it’s too low, you’ll need to top it up using the filling loop, which is usually located underneath the boiler.

7. Turn the Boiler Back On

Once you’ve bled all the air and checked the pressure, you can turn the boiler back on. Monitor the system for any unusual noises or cold spots in the radiators. If everything runs smoothly, you’ve successfully bled the air from your boiler system.

Best Practices for Preventing Air Build-Up

Bleeding your boiler system once or twice a year can help maintain its efficiency. However, you can also take additional steps to prevent excessive air from entering the system.

1. Regularly Check Pressure: Low pressure in the system can lead to air entering the pipes. Keep an eye on the boiler’s pressure gauge and ensure it remains within the recommended range. If the pressure consistently drops, it could indicate a leak or other issues that need professional attention.
2. Install an Automatic Air Vent: An automatic air vent can help eliminate air from the system without manual bleeding. These vents are designed to release air as it accumulates, which can be particularly useful in large commercial systems where bleeding radiators manually can be time-consuming.
3. Schedule Routine Maintenance: Annual boiler inspections and maintenance by a qualified technician can catch issues like air in the system before they become serious. Regular maintenance will also ensure your boiler is running at peak efficiency, saving you on energy costs and extending the life of the system.

When to Call a Professional

While bleeding air from a boiler is straightforward, there are times when it’s best to call in a professional. If you notice that the pressure drops frequently, your radiators are still not heating up after bleeding, or the boiler is making loud, unusual noises, there could be a deeper issue at play. In these cases, hiring a licensed HVAC technician can help diagnose the problem and prevent costly repairs down the road.

Maintaining tenant comfort and managing energy costs is critical to keeping your boiler system efficient. Bleeding air from your boiler is a simple yet essential step in preventing common heating issues. Following the steps in this guide and staying proactive with regular maintenance will ensure your boiler runs smoothly and lasts longer.

However, there’s an easier way to take control of your boiler’s efficiency. With Runwise’s smart controls, you can automate your boiler management, prevent issues before they arise, and optimize performance without the hassle of manual intervention. Ready to make heating problems a thing of the past? Book a Runwise demo today and see how we can help you manage your building’s heating system more efficiently and effortlessly.