I've had my stove for 35 years and never had anything monitoring the cat, that's the way it was sold back then. Didn't know it had a removeable plug until this year when I bought a K type high temp thermocouple to monitor the cat.As you can see, VC went generic with their materials. My Cat probe only indicates when it is ready to be activated so you can shut the damper.
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. Except today I let the morning mini load catch too long and there was that plastic smell again. Stove wasn't exceptionally hot but the stove pipe was. Well at least what was on the glass from overnight is gone now.