How to Check if the Flame Sensor Is Good in an Oil Stove

Start the Stove

• Turn on the furnace. This initiates ignition.

Check for Ignition

• Listen and look that the flame ignited. Use both aural and visual cues, which varies by oil-stove model.

Monitor for Shut-Off

• Wait 20 seconds to see if the furnace automatically shuts off. If the flame ignited and the stove shuts itself off, the sensor is not detecting the flame’s heat. This means it may need cleaning or replacing.

Clean the Sensor

• Turn off power to the furnace. Remove the sensor, which is a small and somewhat delicate-looking device. Rub down the sensor with steel wool, emery or light sand cloth. Replace the cleaned sensor in the unit. Examine the sensor visually while you have it. Replace it if it appears rusty or burned, according to Steve Arnold, owner and president of Arnold Service.

Retest the Sensor

• Test the device once more. If it shuts off again within 20 seconds, buying a new one is in order.

Examining the Cadmium Cell Sensor

• If your oil stove is less than 15 years old, it may be equipped with a cadmium-cell sensor assembly. Testing it requires more steps. Start operating the oil stove and let it run for a few minutes. Open the oil stove or furnace, revealing its controls. Look for the cadmium-cell relay switch, which is typically a small, rectangular box with a red button. The red button is there for testing and reset purposes. Press down on the button while the burner is operating. The system should stop when you depress the button and start again when you release it. If this does not occur, your sensor is not properly functioning. If you want further confirmation, have an expert test the sensor with an ohmmeter, a device that measures electrical resistance. If the sensor is not seeing the flame, the ohmmeter will be close to infinity. If it is working normally, the reading should be 0.5 to 0.6 Ohms. If your sensor assembly is equipped with a self-test monitor, as is the case with some newer oil-stove models, press down on the red button for half a second and observe a series of LED flashes that indicate electrical resistance and correlate to ohm meter readings. More than four flashes means the sensor is malfunctioning. Steve Arnold recommends replacing flame sensors to begin with, as cleaning provides only a temporary fix.