Gas Fitter Practice Test

What could be the cause of a combustion gas odour when the circulating blower activates?

1. Cracked heat exchanger

2. A problem in the air circulating or distribution system

3. The vent or chimney is plugged

4. The filter requires cleaning or replacement

The correct answer is: Cracked heat exchanger

A cracked heat exchanger can lead to a combustion gas odor when the circulating blower activates due to the direct exposure of combustion gases to the air that is being circulated throughout the space. Heat exchangers are designed to separate combustion gases from the indoor air that is heated and distributed by the blower. If there is a crack or hole in the heat exchanger, it compromises this separation, allowing harmful gases such as carbon monoxide or other combustion by-products to leak into the air stream. As the blower turns on and circulates air, these gases may be carried into the living environment, creating a noticeable and potentially dangerous odor. Issues related to the other options may not necessarily result in a combustion gas odor. Problems in the air circulating or distribution system might lead to inadequate airflow but typically wouldn't introduce combustion gases. A plugged vent or chimney could cause backdrafting or inefficient operation but would not usually generate an odor from combustion gases being circulated directly in living spaces. Lastly, a dirty or clogged filter can impact airflow and efficiency but is unlikely to cause an actual combustion gas smell unless it somehow contributed to overheating or other secondary issues.