Which of the following is a sign of a limit switch malfunction?

A limit switch is a safety device in a gas furnace that monitors the temperature within the heat exchanger. When the heat exchanger reaches a predetermined temperature, the limit switch opens, turning off the burner to prevent overheating.

When the furnace does not start at all, it may indicate that the limit switch is malfunctioning. If the switch is stuck in 'open' position due to a fault, the burner won't ignite, causing the furnace to remain non-operational. This is a safety feature designed to prevent damage or hazardous conditions from an overheating furnace.

Being aware of the role of the limit switch helps in diagnosing issues with a furnace. Proper functioning of this switch is crucial for maintaining safe operation. Therefore, a situation where the furnace fails to start can strongly suggest a problem with this crucial safety component.