Who knew there were smoke emitting diodes in the rheostat for the fireplace insert blower?
The fan has two elements to the control system. It has an on/off snap-disk thermostat in series with a speed-control rheostat.
The fan unit is self contained so the on/off element is mounted very low and in the corner of the insert. It is mounted below the insulating material that lines the floor of the firebox.
It takes a long time for the fan to kick "on".
I added an additional snap-disk but that did not prove reliable in the sense that there were still multiple layers of metal and dead-air separating it from the firebox.
So I went old-school. I added a simple 125V/3A rated, on/off toggle switch. While installing the switch, a hot wire touched the blower housing for a fraction of a second which energized the SED in the rheostat.
OK, it was probably not the SED. Most rheostats involve windings of resistance wire and a sliding contact. I probably blew out the resistance wire.
I have not one, but TWO rheostats ordered and jumpered across the defunct speed control. The fan runs in full-on or full-off mode.
Note to self: Next time, unplug the unit before fiddling with the electrical guts of it.