What is the most likely issue if the HSI (Hot Surface Ignitor) does not energize?

If the hot surface ignitor (HSI) does not energize, the most plausible issue is a failure in the power supply. This is typically the first thing to check because without adequate power reaching the ignitor, it will not be able to heat up and ignite the gas. The ignition system relies on a functioning electrical circuit, and if there is no power supply, the entire process is compromised, rendering the ignitor useless.

In contrast, an open air switch might affect the system's ability to ignite, but it would not directly prevent the ignitor from receiving power. A control board malfunction could also lead to various issues, including failure to energize the ignitor, but it essentially acts as a management system that needs the power supply to function properly. Ignition module failure is relevant as well, but in this scenario, it would be secondary to the power supply issue. If the power supply is compromised, no component downstream, including the ignition module or the ignitor itself, will function as intended. Thus, the power supply failure is the critical factor to consider first when diagnosing why the HSI does not energize.