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Cad Cell Replacement & Installation in Connecticut

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What is a Cad Cell?

A cad cell is a component used in oil-fired heating systems to detect the presence of a flame. It is an important safety device that helps ensure the proper operation of the burner and prevents potentially dangerous situations. The cad cell consists of a small, sensitive photoresistor that is capable of detecting light. It is typically located near the burner’s blast tube and is positioned to receive light emitted by the flame. 

Why is a Cad Cell Important?

The cad cell plays a crucial role in ensuring the safe and efficient operation of oil-fired heating systems by providing flame detection and helping to prevent potential hazards.

A cad cell is connected to the burner’s control system, which monitors the signal from the cell. If the cad cell detects the presence of a flame, it sends a signal to the control system indicating that the burner is functioning properly. However, if the cad cell does not detect a flame or the signal is weak, it can indicate a malfunction, and the control system can take appropriate action, such as shutting off the fuel supply to prevent unburned oil from accumulating. 

What Causes a Cad Cell to Malfunction?

Dirt or contamination: Over time, the cad cell’s surface can accumulate dirt, soot, or other contaminants, which can interfere with its ability to detect the flame accurately. This can result in a weak or unreliable signal, leading to malfunctions.

Misalignment: If the cad cell is not properly positioned or aligned with the flame, it may not receive an adequate amount of light emitted by the flame. This misalignment can cause false readings or the inability to detect the flame, resulting in malfunctions.

Deterioration: The cad cell itself can degrade or become damaged over time, affecting its sensitivity and ability to detect light. Exposure to excessive heat, electrical surges, or physical damage can contribute to cad cell deterioration.

Wiring issues: Faulty or loose wiring connections between the cad cell and the control system can disrupt the signal transmission or result in intermittent connections. This can lead to inconsistent readings and malfunctions.

How Do I Know if my Cad Cell is Broken? How Will it Affect My System?

Burner cycling: The cad cell may provide erratic or inconsistent readings regarding the presence of a flame. This can result in the burner cycling on and off frequently or failing to ignite at all.

Delayed or no ignition: A malfunctioning cad cell may cause delays in the ignition sequence or prevent the burner from igniting altogether. 

Frequent system shutdowns: The cad cell’s malfunction can cause the burner to shut down intermittently, even when a flame is present. 

Failure to respond to flame loss: If the cad cell is unable to detect when the flame has gone out, the burner may continue to operate despite the lack of flame. This can cause unburned fuel to accumulate and potentially create safety hazards.

Excessive soot or black smoke: A broken cad cell may not detect flame instability or poor combustion, leading to an excessive buildup of soot or the production of black smoke. This can indicate incomplete or inefficient combustion.

Error codes or indicator lights: Some heating systems have diagnostic capabilities, and a broken cad cell may trigger error codes or indicator lights on the control panel. These codes or lights can help identify a cad cell malfunction.


If you suspect that your cad cell is broken or malfunctioning, it is recommended to contact a qualified heating system technician. They have the expertise to diagnose the issue accurately and can recommend appropriate repairs or replacements for the cad cell if needed. 

Although cad cells are fairly inexpensive devices and simple to replace when they go bad, it is recommended that your cad cell be tested, cleaned, and aligned during annual maintenance visits. This may help catch potential issues before they become a larger issue.