What is one common cause of a gas furnace igniting but not producing heat?

A gas furnace igniting but failing to produce heat often points to issues with the flame sensor. The flame sensor's role is to monitor the flame produced by the burner. When it is functioning properly, it allows the furnace to continue running; if it malfunctions or becomes dirty, it may not detect the flame. As a result, the system can shut off fuel supply, leading to a situation where the igniter lights the gas, but there is no ongoing combustion to generate heat.

For proper operation, the flame sensor should provide a signal back to the control board to ensure that the burner is lit and functioning. If this signal is disrupted, the furnace may start but will not heat effectively, as the system believes there is no flame when there actually is one. Regular maintenance that includes cleaning the flame sensor can help prevent this issue.

In contrast, while other components such as a faulty thermostat, a broken blower motor, and a clogged air filter can lead to heating problems, they would typically produce different symptoms or issues. For example, a thermostat issue might prevent the furnace from igniting at all or operating at the desired temperature, while a broken blower motor wouldn't circulate the heat even if the furnace is operating. A clogged air filter primarily affects airflow,