Is your oil boiler not performing efficiently? Wondering why your heating bills are skyrocketing? It might be time to learn how to bleed an oil boiler. Regular maintenance, like bleeding the bleeder valve and restarting, can prevent breakdowns and improve the performance of radiators, thermostat, and furnace.

When air bubbles infiltrate your heating system, they hinder the flow of hot water in your radiators, making your boiler work harder and consume more energy. By bleeding your oil boiler using a bleeder valve, you release trapped air and allow for smoother operation.

This simple process, along with checking the thermostat, can significantly enhance efficiency while keeping those pesky utility bills in check.

Don’t overlook this crucial step in maintaining your oil boiler’s health. In this guide, we’ll dive into the nitty-gritty of bleeding an oil boiler, including the bleeder valve, radiators, furnace, and thermostat, and explore how it can save you both money and headaches. So let’s get started on maximising your heating system’s potential!

Tools Needed for Bleeding and Restarting an Oil Boiler

Essential Tools for the Process

To successfully bleed and restart an oil boiler, it is crucial to have the right tools, such as a bleeder valve, at hand. These tools will ensure a smooth and efficient process, allowing you to get your boiler, radiators, and furnace up and running in no time. Make sure to consult a heating engineer for assistance if needed.

  1. Bleed Key: The first tool you will need is a bleed key. This small metal key is specifically designed to open the bleed valve on your oil boiler. It allows air trapped in the system to escape, ensuring proper circulation of fuel.
  2. Container: When bleeding an oil boiler, some fuel may spill out along with the air bubbles. To prevent any mess or wastage, have a container ready to catch any spilled fuel. A small bucket or pan should suffice.
  3. Cloth: In addition to a container, keep a cloth nearby to quickly wipe up any spills or drips that may occur during the bleeding process. This will help maintain cleanliness and prevent slippery surfaces.
  4. Pressure Gauge: While not essential, using a pressure gauge can be beneficial when bleeding an oil boiler. It allows you to monitor the system pressure accurately, ensuring it remains within the recommended range throughout the process.
  5. Adjustable Wrench: Lastly, have an adjustable wrench on hand. This tool will come in handy if you need to open or close valves during the bleeding process. It provides flexibility in handling different types of valves commonly found in oil boilers.

By having the right tools for restart and tubing readily available before starting the procedure, you can proceed confidently without interruptions or delays. It is important to ensure that you have obtained proper consent before proceeding.

Step-by-Step Guide: How to Bleed an Oil Boiler

Locating the Bleed Valve

To effectively bleed your oil furnace, you need to start by locating the bleed valve on your heating system. The bleed valve is typically located near the top of the furnace and can be identified as a small metal screw or knob. It’s important to note that different furnaces may have slightly different designs, so consult your furnace’s manual for specific instructions if needed.

Using the Bleed Key

Once you have located the bleed valve, it’s time to use the bleed key. The bleed key is a specialised tool designed to open and close the valve easily. If you don’t have a bleed key, you can usually find one at a local hardware store or online.

Insert the bleed key into the valve of your furnace and turn it counterclockwise slowly. This will gradually open the valve and allow any trapped air to escape from your oil boiler system. As you do this, listen carefully for any hissing sounds which indicate that air is being released from the bleeder.

Releasing Trapped Air

As you continue turning the bleeder key counterclockwise, keep an eye out for any air bubbles coming out of the valve. It’s essential to release all trapped air from your furnace system as it can affect its efficiency and performance.

If there are air bubbles present in your oil furnace or boiler pressure system, let them escape until fuel starts flowing steadily without any signs of air. This ensures that only pure fuel, free from any contaminants, remains in your system, allowing your burner and oil filter to operate optimally.

Closing the Valve

Once you’ve successfully bled your oil boiler and ensured that the burner is functioning properly, it’s time to close the valve. Turn the bleed key clockwise gently until it is fully closed, ensuring that the pressure is stable.

Be cautious not to overtighten or force the bleed screw closed as this could damage both the valve and your oil furnace’s boiler pressure.

Congratulations! You’ve successfully completed the bleeding process for your oil boiler. Regularly bleeding your boiler can help maintain the system’s efficiency and prevent potential issues caused by trapped air. Now, it’s time to restart the furnace and ensure it keeps running smoothly.

Remember, safety should always be a priority when working with an oil furnace. If you’re unsure about any step or encounter difficulties during the bleeding process, it’s advisable to contact a professional technician who can provide expert assistance. 

Troubleshooting: Restarting a Furnace After Running Out of Heating Oil

Running out of heating oil can be a frustrating experience, especially when it causes your furnace to stop working. However, restarting the furnace immediately after refilling the tank is not recommended. 

When your oil furnace stops working due to running out of heating oil, it is essential to understand the steps involved in restarting it properly. Rushing into the process without taking necessary precautions can lead to further issues and potential damage to your oil furnace. 

One crucial reason for not immediately restarting the oil furnace after refilling the tank is that air may have entered the fuel lines during the outage. This air needs to be purged from the system before starting up the oil furnace again. Failure to do so can result in poor burner performance and even complete system failure.

To ensure a safe restart of your oil furnace, consult the manufacturer’s manual or contact a qualified technician who can provide you with specific instructions tailored to your appliance model. They will guide you through each step required for bleeding air from the fuel lines and priming the system correctly. 

Clogged filters are another common issue that may arise after running out of heating oil. These filters, designed to trap impurities present in the fuel supply, can obstruct proper functioning when they become clogged due to prolonged use without adequate fuel supply. 

If you suspect a clogged filter as the reason for your furnace malfunctioning after refilling with oil, it is best to seek professional assistance. A trained technician will have the necessary tools and expertise to restart, clean or replace these filters efficiently.

Airlocks are yet another potential problem that may occur during restarts after running out of heating oil. Airlocks happen when air becomes trapped within certain parts of the fuel system, hindering the flow of oil. This can prevent your furnace from igniting or cause it to shut down unexpectedly. 

To address airlocks in an oil furnace, technicians often use a process called bleeding, which involves releasing trapped air from specific points in the fuel system. It is crucial to let professionals handle this task as they have the experience and knowledge to safely and effectively restart the oil furnace. 

Safety Measures: Turning Off and On the Furnace for Bleeding

Safety should always be your top priority when running the v4 system. 

Safely shut off power supply before performing any maintenance on your furnace or boiler.

Before starting any work on your oil boiler, make sure to turn off the power supply. This step is essential to prevent any accidents or injuries while working with electrical components. Locate the main power switch near your furnace or boiler and switch it off. If you are unsure about its location, consult the user manual or contact a professional for guidance. To restart the boiler after completing the necessary maintenance, simply switch the power back on. Additionally, refer to the accompanying image for a visual guide on restarting your boiler. Once the power is back on, your boiler should be up and running again.

Follow proper safety protocols when turning off gas or electricity connections during the bleeding process.

During the bleeding process, it is crucial to turn off both gas and electricity connections to ensure a safe environment. Start by shutting off the gas valve leading into your furnace. This valve is typically located near the unit’s fuel line connection. Turn it clockwise until it is fully closed. Refer to the image below for visual guidance.

Next, locate the electrical disconnect switch that controls power supply to your furnace or boiler. Flip this switch into the “Off” position to cut off electricity flow and restart the running system. By following these safety protocols, you minimise potential hazards associated with gas leaks or electrical malfunctions during maintenance. See the image below for reference.

Take precautions while handling hot components during the bleeding process.

When dealing with an oil furnace, several components can become hot during operation. It is important to exercise caution while handling these parts when restarting the furnace. Use heat-resistant gloves or wait until they cool down before attempting any adjustments.

One critical component you may encounter while bleeding an oil boiler is the bleeder valve or bleed screw. This valve allows air trapped in the furnace system to escape and should be opened slowly using an appropriate tool. Remember to exercise caution and avoid touching the valve directly after it has been running, as it can become extremely hot. See the image below for a visual representation.

Make sure all valves are closed before restarting the furnace.

After bleeding the air from your oil furnace, it is time to restart the system. However, before doing so, ensure that all valves used during the bleeding process are closed tightly. This step prevents any potential leaks or malfunctions once you turn on the power supply again. 

Once you have confirmed that all valves are securely closed, proceed to turn on the power supply for your furnace or boiler. Refer to your user manual for specific instructions on how to safely restart your particular running model. 

By following these safety measures when turning off and on your furnace for bleeding, you can ensure a secure environment for performing maintenance tasks on your oil boiler. Remember to prioritise safety and consult professionals if you encounter any uncertainties or complications during the restart process.. Running smoothly again, your oil boiler will be ready to provide efficient heating.

Comparing Oil and Gas Boilers: When to Bleed and Restart

Understanding the Differences

To properly maintain your furnace, it’s essential to understand the differences between oil and gas boilers. While both systems serve the same purpose of providing heat, their mechanisms differ significantly. Image: Furnace running. To ensure smooth operation, learn how to restart your furnace if needed.

Knowing When to Bleed an Oil Boiler

There are specific instances where the furnace becomes necessary. Unlike gas boilers, oil boilers require occasional bleeding to remove trapped air from the system. This is crucial for ensuring optimal performance and preventing potential issues such as reduced efficiency or even complete breakdowns. The image of a running furnace can help illustrate this process. If the furnace stops running, a restart may be needed.

To determine when it’s time to bleed your oil furnace, keep an eye on the pressure gauge. If you notice a significant drop in pressure or if the gauge indicates low pressure, this may indicate air pockets within the system. In such cases, bleeding becomes necessary to restart proper functionality. 

Maintenance Requirements for Each Type of Heating System

Maintaining a heating system, such as a furnace, involves different requirements depending on whether you have an oil or gas boiler. Understanding these distinctions will help you ensure that your furnace operates smoothly throughout its lifespan. 

For oil boilers:

  1. Regularly check the oil level in your tank to ensure it is running smoothly. Refill as needed to prevent any issues with restarting the furnace.
  2. Schedule annual inspections with a professional technician who can clean and service your oil furnace unit. This will ensure that your unit remains in optimal running condition and is ready to restart when needed.
  3. Monitor the oil furnace flue pipe for any signs of soot buildup or obstructions. Restart the oil furnace if necessary. Keep an eye out for any issues by visually inspecting the flue pipe image. Ensure that the oil furnace is running smoothly.
  4. Keep an eye on oil furnace fuel filters and replace them as recommended by the manufacturer to ensure smooth running and avoid the need to restart.

For gas boilers:

  1. Regularly check for any gas leaks in your oil furnace by using a mixture of soapy water.
  2. Ensure proper ventilation by keeping air vents unobstructed.
  3. Have annual maintenance performed by a qualified technician to ensure safety and efficiency of your oil furnace. If you need to restart your oil furnace after it stops running, get in touch with us!
  4. Consider installing carbon monoxide detectors near your gas furnace for added peace of mind. These detectors can help ensure the safety of your home while your furnace is running. 

Additional Steps and Precautions for Gas Boilers

While both oil and gas boilers require regular maintenance, there are a few additional steps and precautions to keep in mind when dealing with gas boilers. One important aspect of gas boiler maintenance is ensuring that the furnace is running smoothly. If you encounter any issues with the furnace, it may be necessary to restart it. 

  1. Gas boiler pressure: Unlike oil boilers, gas boilers operate under specific pressure requirements. It’s crucial to maintain the recommended pressure levels to ensure proper functioning of the furnace. Regularly check the pressure gauge and consult your manufacturer’s guidelines for optimal pressure ranges. If your furnace stops running, you may need to restart it.
  2. Gas furnace safety checks: Due to the combustible nature of natural gas, it’s essential to prioritise safety when dealing with gas furnaces. Conduct regular gas safety checks, including inspecting the flue system and ensuring proper ventilation, to minimise any potential risks. Additionally, make sure to regularly run your furnace and restart it if needed.
  3. Professional assistance is recommended for more complex issues or annual servicing of your gas furnace. While homeowners can handle some maintenance tasks, seeking professional help ensures safety measures are followed and the system runs efficiently. 

By understanding the differences between oil and gas furnaces, as well as their respective maintenance requirements, you can ensure optimal performance and longevity for your heating system. Regularly monitor pressure levels, schedule professional inspections, and address any issues promptly to keep your furnace running during those chilly winter months. 

Refilling the Fuel Tank and Completing the Process

After successfully bleeding your oil boiler, it is important to refill the fuel tank before you can restart the furnace. 

Here are some essential steps to follow in order to complete this process effectively:

Step 1: Follow proper safety guidelines while handling and storing heating oil.

When working with a furnace, it’s crucial to prioritise safety. Always wear protective gloves and eyewear when running the furnace to prevent any contact with your skin or eyes. Ensure that you are working in a well-ventilated area to avoid inhaling any fumes. 

Step 2: Use clean, high-quality fuel for optimal performance.

To guarantee efficient operation of your oil furnace, make sure you use clean and high-quality fuel. Contaminated or low-grade fuel can lead to clogs in the fuel line or damage the internal components of your furnace. Regularly check your oil tank for any water accumulation or sediment buildup that could affect the quality of your fuel. 

Step 3: Refill the fuel tank using appropriate techniques.

To refill your fuel tank:

  1. To restart a furnace, locate the fill pipe on top of your oil tank. If you need guidance on how to restart a furnace, you can refer to the instructions. Once you have located the fill pipe, make sure the furnace is running properly.
  2. Remove the cap from the fill pipe.
  3. Attach a funnel securely into the fill pipe opening.
  4. To restart an oil furnace, slowly pour the fuel into the funnel, making sure there are no spills or overflows. 
  5. Monitor the level gauge on your oil tank to prevent overfilling and ensure proper functioning of your furnace. 
  6. Regularly checking the gauge will also help you keep track of how much oil is left in the tank, so you can avoid running out and keep your furnace running smoothly.

Step 4: Check for any leaks or issues before restarting.

Before restarting your oil furnace, it’s crucial to inspect all connections and components for any potential leaks or issues. Inspect all visible pipes and tubing connected to the furnace for signs of damage or leakage. 

  • Ensure that all valves are properly closed and tightened.
  • Check if there is proper flow of fuel from the oil furnace pump through each pipe by observing its movement visually.
  • Look for any abnormal noises or vibrations that could indicate a problem with the oil furnace fuel pump or supply. 

Step 5: Restart your oil boiler and monitor its performance.

Once you have refilled the fuel tank of your oil furnace and ensured there are no leaks or issues, it’s time to restart your oil boiler. Follow the user instructions provided by the manufacturer for restarting the system. Monitor its performance closely, paying attention to any unusual behaviour such as inconsistent heating or frequent shutdowns. 

Regular maintenance is essential to keep your oil furnace running smoothly. Be sure to schedule routine inspections and cleaning to prevent potential problems in the future. If you encounter any persistent issues or fixes beyond your expertise, it may be necessary to consult a professional technician for further assistance. 

By following these steps and guidelines, you can confidently restart your furnace after bleeding an oil boiler, ensuring optimal energy efficiency and reliable heating throughout your home.


Congratulations! You now have all the knowledge and tools you need to successfully bleed and restart your oil heating system. By following the step-by-step guide, you can ensure that your furnace is functioning efficiently and effectively.

Remember to prioritise safety when working with your furnace. Always turn off the power before starting the bleeding process, and follow the necessary precautions.

It’s important to note that while gas furnaces do not require bleeding, it’s crucial to understand the differences between oil and gas systems. Knowing when to bleed and restart your oil furnace will help maintain its performance and prevent any potential issues. 

Once you have successfully bled your oil furnace, don’t forget to refill the fuel tank to complete the restart process. This ensures a continuous supply of heating for your home. 

In conclusion, by regularly bleeding your oil boiler and restarting the furnace, you can optimise its efficiency, save money on energy bills, and prolong its lifespan. It’s a simple maintenance task that can make a significant difference in keeping your home warm during those cold winter months. 

So why wait? Grab those tools and take control of your oil furnace heating system today!

Frequently Asked Questions

It is recommended to bleed an oil furnace at least once a year or whenever you notice reduced heat output or strange noises coming from the system. 

Yes! Bleeding an oil furnace is a relatively simple task that can be done by homeowners themselves. 

If you neglect regular bleeding of your oil furnace, it can lead to reduced efficiency, increased fuel consumption, and potential damage to the system.

The time required to bleed an oil furnace boiler can vary depending on the size of your system and the amount of air trapped inside. On average, it takes around 15-30 minutes.

Yes, common signs of furnace issues include cold spots in radiators, gurgling or banging noises, and reduced heat output. If you notice these symptoms, it’s time to bleed your oil boiler. 

When maintaining your furnace, it is important to use high-quality heating oil specifically designed for boilers. Consult with your local supplier for the most suitable option.

Yes, you can bleed your oil furnace during winter. However, ensure that you have enough heating oil in your tank before starting the process.

While bleeding the furnace, some minor spills may occur. However, if done carefully, it is generally not a messy task. It’s always a good idea to keep absorbent materials nearby just in case.

It is advisable to wear protective gloves and safety glasses when working with your furnace. This will help prevent any accidental injuries or exposure to hot components.

Remember, if you ever feel unsure about performing any maintenance tasks on your oil furnace, it’s always best to consult a professional technician for assistance.