Oilheat Systems: All About Control

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 Connecticut and throughout the Northeast.

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 advances in equipment technology. 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 air temperature, water temperature and pressure control. There are two categories: high limit/safety controls and low limit/operating controls.

High limit/safety controls: These 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 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, which allows the homeowner to try to 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 sensor), were added to oilheat systems in the early 1970s. A cad cell uses its photocell “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 a house’s basement stairs. If a home’s 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 Wi-Fi-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.

For more information about how heating systems work and what to know when inspecting heating equipment, consider requesting the free “Home Inspectors’ Guide to Oilheat.”