What Is A Cad Cell?

A cad cell is an electric eye that sees the flame on power burners. In the old days, oil fired appliances had these stack relay switches that would rely on a bi-metal to heat up and prove the burner was actually igniting the fuel.

Nowadays, the Primary Control utilizes a Cad Cell. It sees the flame and translates the electrical resistance (ohms) into a reading that the primary control decides whether the burner is safe to keep running (the flame is on), or the burner needs to be shut down (there is no flame, or there is a poor flame).

Some of today's oil burners are sensitive to too much draft. There may indeed be a flame, but because the excessive draft is pulling on the flame, the cad cell cant get a proper reading and shuts the burner down.

To think of how important the Primary Control is, and its associated cad cell, if the flame doesn't light for whatever reason (ignition is faulty, fuel pump is defective, oil filter is clogged, etc), the burner could potentially keep sending oil (or gas, depending on the fuel being burned) into the combustion chamber. This would be a very dangerous condition.