Ultraviolet control panels dissipate real heat from ballasts and ignitors into a largely sealed enclosure. Cooling failures present as intermittent, temperature-dependent shutdowns rather than as a clean fault, so airflow parts are worth replacing on condition rather than on failure. This is the small fan that cools the control board itself rather than the enclosure. Board-mounted fans are easy to overlook at service and their failure raises local board temperature without necessarily tripping a cabinet thermostat.