Heating System Oil Burners
Inspection, Tuning & Repair Guide

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Oil burner installation, troubleshooting, diagnosis & repair guide: here we provide a detailed guide to oil burners used on heating systems, boilers & furnaces: basic parts, operation, maintenance, repair, performance and heating cost money-saving tips.

We also discuss: How oil burners work: sequence of operation, oil burner safety controls. How to inspect & repair or replace/upgrade oil burners - homeowner basics, service technician basics, diagnosis, repair. Cleaning & maintenance guide for heating system.

This article series answers most questions about central heating and water heating systems and provides guides for troubleshooting, inspection, diagnosis, and repairs.

We also provide an ARTICLE INDEX for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Installation & Diagnostic Guide to Oil Burners for Boilers, Furnaces, & Water Heaters

Oil fired heating equipment such as hydronic (hot water) boilers, steam boilers, warm air furnaces, and water heaters, have used heating oil, usually No. 2 heating oil, and various types of oil burners to burn the fuel, thus providing a heat source for nearly 100 years.

This article describes the basics of how oil burners work, and we provide a guide to their inspection and problem diagnosis and repair.

Oil Burner Manuals - go directly to OIL BURNER MANUALS

Boiler Controls - go directly to BOILER CONTROLS & SWITCHES - controls used on all brands of heating boilers

Furnace controls - go directly to FURNACE CONTROLS & SWITCHES

How Oil Burners Work

Refer to the schematic of a conventional oil burner shown below, where we list the major parts parts of a modern oil burner. The sketch at above left is courtesy of Carson Dunlop Associates.

If you need to diagnose and fix an oil fired heating equipment problem with your oil burner, read the text below but also be sure to check out the detailed oil burner articles listed at the ARTICLE INDEX at the bottom of this article


Sequence of steps in home heating or hot water heater oil burner operation:

  1. Electric power on:

     In response to an aquastat or other heating boiler, furnace, or water heater control, electrical power to the oil burner is switched "on".


    Electricity is connected through a safety control such as the Cad Cell relay labeled "primary controller" in the sketch.

    Details: AQUASTAT CONTROLS, Cad Cell Relay,


  2. Oil burner electric motor starts: The primary controller permits electrical power to flow to the electric motor shown on the right side of the oil burner, causing the motor shaft (not shown) to rotate.


  3. Oil burner's Electric Motor shaft rotates, driving other parts through a coupling: 

    the spinning shaft of the electric motor extends horizontally through the inside of the oil burner motor where it is coupled first to a rotating squirrel cage fan - the oil burner's air blower (providing combustion air), and second to the the air blower and oil pump (fuel unit).

    High speed oil burner motors spin at 3450 RPM. Older "low speed" (and quieter) oil burners use an electric motor rotating at 1725 rpm.

  4. Combustion air: 

    Oil burner blower fan spins, drawing combustion air through adjustable air intake slots on the left side of the oil burner, and simultaneously,

  5. Heating oil delivery:

    the electric motor shaft extension drives the oil pump (fuel unit) shown on the left-most side of the oil burner in the sketch. The oil pump (oil burner fuel unit such as a Sunstrand™ fuel unit) draws heating oil from the oil tank through a fuel line connected to the oil tank (hopefully through an external oil filter and an internal filter screen) and pressurizes the heating oil to 100 psi or more.

    Pressurized heating oil flows out of the oil pump thorough a high pressure oil line into the oil burner tube where it is converted to a fine spray by an oil nozzle attached to the end of the nozzle assembly. Problems with the heating oil fuel unit can lead to loss of heat, noisy operation, and other oil burner operating troubles.

    Details about fuel units (heating oil pumps) and their installation, diagnosis, or repair are



  6. Heating oil ignition:

    electricity is also delivered to an ignition transformer (the black box on top of the back of the oil burner).

    The ignition transformer converts the incoming 120V electrical power to very high voltage which is fed to two electrodes attached to the nozzle assembly.

    The oil burner nozzle electrodes, separated by a small gap, produce an electrical spark (usually continuous or "continuous ignition oil burner operation" vs. "intermittent ignition" on some older systems) which is right in the path of the oil being sprayed by the oil burner nozzle, causing the oil to ignite.

    Safety controls will turn off the oil burner if flame ignition is not successful. This feature prevents continuing pumping un-burned heating oil into the system.



  7. Heating oil combustion:

    the sprayed, burning heating oil heats the interior of the furnace, boiler, or water heater combustion chamber which is normally lined with a material whose surface will get very hot but won't burn.

    The combustion chamber liner prevents the oil burner from damaging the cast iron or steel boiler itself, while the hot surface of the combustion chamber liner helps make sure that all of the fine droplets of oil sprayed into the combustion chamber do in fact ignite.

    Also see COMPLETE COMBUSTION, STOICHIOMETRIC for an explanation of complete fuel combustion and boiler or furnace maximum efficiency.

  8. Heat transfer: 

    hot combustion gases from the burning heating oil flow (usually upwards) through the furnace, boiler, or water heater heat exchanger where they transfer heat to that appliance before continuing to flow through a flue vent connector (stack pipe) and then outside through a chimney.

    See: BOILERS,



  9. Electric power and oil burner off:

    when the aquastat, thermostat, or other primary control senses that the desired temperature has been reached, electric power to the oil burner is turned off, stopping the electric motor from spinning, thus stopping the combustion air blower, oil pump, and turning off the ignition transformer.



Installing a New Oil Burner

Reader Question: We want to install a new oil burner but we don't want to get "robbed"

We have an oil burner that is in the house since 1966. I want to buy a new one that will save us money each month on oil and at the same time be effective, as well as heat up our house

. Do you know some names or dealers? I also do not want to get taken or robbed.

We also want to have the sludge taken out of our oil tank, can you recommend someone for both these services.

We live on long island and are seniors. - M.P., Rockville Centre, Long Island

Our photo above shows an antiquated cast iron Arco™ boiler that was converted from coal to oil.

The oil burner on this unit was itself an antique, low-speed unit - though not the system named above nor the upgraded oil burner system described below.

Reply: here are some things to check before upgrading an oil burner

A competent onsite inspection of your entire heating system and chimney, performed by an expert usually finds additional clues that help accurately diagnose a problem or might make clear if upgrading the oil burner on your heating system makes sense. That said, here are some things to consider:

Before even considering a new oil burner, you will want a thorough inspection of your boiler or furnace to be sure it's in good enough condition to be worth the investment.

For example if the heater is badly rusted or cracked, it needs to be replaced.

If the heater itself is in good condition, the replacement burner can improve its efficiency and save you money. Our photo (left) shows a modification we [DF] performed to a large cast-iron heating boiler in New York.

The original low-speed oil burner was fired into the very bottom of a quite large, 1930's vintage cast iron boiler that was in good condition but running at the low 70% efficiency range. Originally this had been a coal-fired boiler, converted to burn oil. The original oil burner fired into the bottom of a large combustion chamber.

After inspecting the boiler to confirm that it was not damaged, we installed a new Beckett™ oil burner, firing it up through a higher door on the heating boiler.

The system efficiency increased from around 71% (after cleaning and tuning) to 82% efficiency (also after cleaning and tuning) - a heating fuel cost savings improvement of 11 percentage points, but actually a15% reduction in heating oil cost.

We can't make specific contractor referrals for oil burner upgrades nor service. But you can make these efforts to steer clear of a bad experience:

Oil Burner Manuals & Guides for Boilers, Furnaces, Water Heaters

The manuals previously listed alphabetically on this page got promoted!

See OIL BURNER MANUALS OIL BURNER MANUALS - free download manuals for oil burners, controls, fuel units, etc.


Oil Burner Primary / Safety Control Manuals



Continue reading at OIL BURNER INSPECTION & REPAIR or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see OIL BURNER FAQs - questions & answers posted originally on this page

DIAGNOSE & FIX HEATING PROBLEMS-BOILER (hot water or steam heat)


Or see these

Oil Burner Articles

Suggested citation for this web page

OIL BURNERS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this


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