Red Seal Gasfitter — Class B Practice Exam

What does a flame sensor do in a gas appliance?

1. It regulates the flow of gas

2. It detects the presence of a flame to prevent unsafe gas accumulation

3. It ignites the gas for combustion

4. It measures the gas pressure

The correct answer is: It detects the presence of a flame to prevent unsafe gas accumulation

A flame sensor plays a crucial role in the safety and functionality of gas appliances by detecting the presence of a flame. Its primary purpose is to ensure that the appliance operates safely by monitoring whether a flame is present when gas is being supplied. If the flame sensor does not detect a flame, it triggers safety mechanisms that shut off the gas supply, preventing the accumulation of unburned gas, which could lead to a potentially hazardous situation such as an explosion or gas leak. This function is essential for maintaining safe operation since gas appliances typically require a continuous flame for combustion. The absence of a flame while gas is flowing indicates a malfunction or unsafe condition that needs immediate attention. Therefore, when the flame sensor detects the flame, it allows the appliance to operate normally; however, if not, it takes actions to eliminate dangers, highlighting the importance of this component in the overall safety of gas appliances.