A flame sensor is designed to regulate the flow of gas from a gas valve, much like a thermocouple. Testing one is essential to maintaining proper and safe functionality of a gas-powered device regulated by a flame sensor, such as a gas dryer, furnace or water boiler. A malfunctioning flame sensor could cause permanent damage to the device, irregular function and a serious fire. Fortunately testing a flame sensor is straightforward, requiring just a multimeter and a light source.

Step 1

Locate the flame sensor on the gas-powered device; it's usually found inside a small back or front access panel.

Step 2

Unplug the device or, if the device cannot be unplugged, switch the breaker inside the breaker box responsible for the device to the "Off" position.

Step 3

Unfasten the clamp securing the flame sensor in place using a Phillips screwdriver and disconnect the leads by pulling on the wire boots.

Step 4

Set the multimeter to show resistance and touch the probes to the blue and white wire ports on the flame sensor; the multimeter should show low resistance.

Step 5

Press the open end of the flame sensor against a 60-watt light bulb or a flame sensor test lamp. Inspect the multimeter; it should now show high resistance.

Step 6

Replace the flame sensor if the multimeter doesn't show any discrepancy in resistance when the open end of the flame sensor is placed against a light source.