Fan - suddenly full speed only

So i was watching the fire tonight in my Montpelier when i heard a slight popping sound and then my fan speed suddenly increased from medium to full blast, and now the fan speed knob has no effect. i can still turn the fan off, but if it is on it is full speed in any position.

for someone not electrically versed, what can i check or replace to fix this? i assume its the rheostat but not sure if it can just be replaced with something off the shelf or would i need a VC part or what?

Thanks guys. Not sure when I'll have time to take the fan out. It isn't hard to do, per see, but a pain as you have to lower the leveling screws (by hand with an Allen wrenches, a very slow process), then sort of wiggle/fight it out. Would be more inclined to do it but our dishwasher went on the fritz same day (ugh) so that needs to be addressed first.

Is there a way to control fan speed at the outlet end? Like a rheostat outlet or programmable rheostat? I'd love to be able to regulate fan speed either based on a programmable time setting (i.e. run on high for 2 hours after reload, then medium for 4 hours, then low after that) or based on external input (like the output of an auber stove thermocouple)

ShawnLiNY said:

Remove and clean fan shafts and reoil bearings while changing speed control ( blower controls will burn out and fail faster when debris slows fan resulting in more electrical load at slower speeds ) the high speed is a failsafe ( automotive heater blowers are the same ) chances are the fan is not proprietary to Vermont castings so after removal you can cross reference the manufacturer or part #

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Will do. Had just cleaned it before this season but I don't know how old this is as I got the insert used.

Probably a basic question but what kind of oil do you use on the bearings?