How an Oilheat System Works

The proven reliability of modern oil heating controls has been an important factor in making today’s oilheat a remarkably safe and efficient fuel for heating homes in Wisconsin and elsewhere.

A wide range of limit controls, thermostats and switching relays are used in oilheat systems. They have become more accurate and sophisticated with the introduction of more technologically advanced equipment. Here’s a brief overview of some of the controls to give you a deeper understanding about how an oilheat system works.

Limit controls

Limit controls on oilheat systems regulate warm air, water temperature and pressure control. There are two categories: high limit/safety controls and low limit/operating controls.

High limit/safety controls: These controls act as safeguards to prevent overheating. They will turn off the burner if temperatures become too high in the furnace or boiler, or if the pressure in a steam boiler rises to an unsafe level.

Low limit/operating controls: These controls start and stop the burner on a signal from the thermostat or aquastat (a device that controls water temperature).

Primary controls

Primary controls monitor the oil burner’s flame and modern ones are very accurate. Primary controls also have a reset button. This button allows you to try and restart the burner should a problem cause the unit to shut down.

Cad cell controls

Additional protection circuits, such as the cad cell (cadmium sulfide photocell sensors) were added to oilheat systems in the early 1970s. A cad cell uses its photo cell “eye” to send a shutdown message to the primary control board if it can no longer “see” the burner’s flame.

Burner power switches

There are usually two switches that will cut off power to the burner. A red emergency switch is typically located at the top of the basement stairs. If the heating system is located in a utility room, look for the emergency switch near the room’s entrance. A second burner power switch is often found on or near the heating system.


Many people are now using a smart thermostat in their oil-heated homes. A WiFi enabled thermostat allows homeowners to view and change temperature settings from their smartphone or tablet. Once the smart thermostat gets installed, the homeowner registers it online. This enables access from any location.

Besides all of the controls noted above, many new oil boilers now incorporate energy-saving controls that greatly reduce fuel usage by as much as 10% and provide a more even heat. Meanwhile, high-efficiency oil furnaces now feature variable speed motors that use about 80% less electricity to operate.

Read more about oilheating systems.