What condition causes the temperature limit safety switch to shut off the burner?

The temperature limit safety switch is designed to protect the heating system by ensuring that the temperature within the heat exchanger does not exceed a predetermined safe level. When the heat exchanger becomes overheated, it can lead to dangerous conditions such as heat damage, potential fires, and efficiency losses. The primary role of the temperature limit safety switch is to monitor the temperature of the heat exchanger and shut off the burner if it detects that the temperature is exceeding safe thresholds.

In this context, overheating can occur for various reasons, but a common one is fan motor failure. The fan is responsible for circulating air across the heat exchanger to prevent it from overheating. If the fan motor fails, airflow decreases significantly, which hinders the cooling effect on the heat exchanger, resulting in excessive temperatures. Thus, the temperature limit safety switch responds appropriately by shutting off the burner to prevent further overheating and potential hazards.

It is essential to focus on the function of the safety switch in relation to overheating rather than simply considering other factors like gas pressure or air circulation. Excessive gas pressure can create performance issues, and clogged air filters can restrict airflow, but they do not directly trigger the temperature limit safety switch in the manner that an overheating heat exchanger does.