>  a thermowell in the lid and extending to just above the paddles

It's not a pressure vessel.  The paddles have braces to the shaft that make
any vertically dropped probe  / thermowell unsuitable for all but the
highest liquid levels. I even thought of dangling a probe in on flexible
cable and letting it ride over the paddles but I fear this won't be
accurate or robust at all.

I'll stick a probe in the space above the heated liquid to see what
temperature it does get to - there is a foil extraction duct right there
that gets warm but not hot to the touch. Maybe radiated heat well be a
bigger issue? Only one way to find out.
--=20
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