well, the fire box sits on a "hearth" made of slate and has no electrical connections.
it has a flue that passes through the roof, but that has nothing electrical in it either...
when i was observing the error reads, the steel braided sheath was probably touching the fire box and so was the probe tip.
my multimeter showed no continuity between any of these things, but i removed the braided sheath regardless... and it seems to have solved the issue to a large extent... we'll have to see how it goes after a few more nights of fire...
if you short the thermocouple it gives an error read, (but i didn't try it with a piece of copper wire)