How to bleed an oil burner

How to bleed an oil burner

It is sometimes necessary to bleed air between the oil supply and the burner of an oil-fired boiler. This procedure is usually required after the system has run out of oil and the burner has ‘locked out’ and stopped. After the tank has been re-filled, the air trapped in the oil pipe needs to be released so that fuel can reach the burner and allow it to re-start. This blog is designed to talk you through the steps involved in bleeding a burner…

It is always advisable for homeowners to keep a regular eye on the amount of oil in their fuel tank and to get it topped up before it runs out. If the oil supply feeding the boiler does run out, air can become trapped in the fuel supply line between the tank and boiler. Consequently, after the fuel tank has been filled, it is likely that the burner will not start but will ‘lockout’ – this will be indicated by the lockout button on the front of the burner being lit red.

If this ‘lockout’ occurs, it is recommended that that oil supply to the burner is bled. This process, which is very simple and takes less than five minutes to complete, can be carried out by either the user of the boiler or a heating engineer. Please note, if you are the user and do not feel comfortable with bleeding the burner yourself, please contact your local heating engineer who will be able to assist.

What is required
To bleed an oil burner, three things are required: a flat head screwdriver, a 4mm Allen Key and an old cloth or rag.

The steps involved
Firstly, identify the burner. It has a red plastic cover and is located at the lower part of the boiler (with most boilers, it will be inside the boiler casing). Check to see if the burner lockout button is lit red, indicating that it has locked out. Using the flat head screwdriver, undo the screws and remove the red case on the burner. On most burners there are two screws - one on the front and one on the top of the casing. On larger burners, there are three screws – one of the top and one on each side.

Then, identify the oil pump. This is located on the left side of the burner and is connected to the flexible oil line. After identifying the oil pump, the next step is to find the 3” long hexagonal stem that points outwards from the pump. This has a small threaded plug screwed into the end. Using the 4mm Allen key, unscrew this plug no more than half a turn (180 degrees) and leave the Allen key in place. Please then hold the cloth or rag immediately under the plug to catch any oil that will be released.

The next step is to press the ‘lockout’ button. Please note (this is important), the burner fan will run for a period of 12 seconds and some oil will come out from the loosened plug – please catch this using the cloth or rag. As soon as a buzzing noise is heard, tighten up the threaded plug with the Allen key. If enough air has been bled from the burner, it will fire. If the burner does not fire, but goes to lockout again, please repeat the process.

Why it is important
This procedure is important because it not only helps successfully remove any air trapped in the oil supply to the burner, allowing it to start, but it can help protect the burner. If the ‘lockout’ button is repeatedly pressed after a system runs out of oil, but the cause of the problem is not resolved, this can damage the burner. However, if the above bleeding process is successfully completed, the system’s operation can continue smoothly without causing damage to the burner.

If you have any questions, please contact our Technical Department on 01380 736920.

How to bleed an oil burner
Phil Stanley
Training Manager at Grant UK
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