I'm fairly sure my model doesn't have the electrical cutout you describe,
didn't see anything on the HX pipes when I looked the other day*, plus it
doesn't have an electrical connection (;-).

The flavour of cutout I was on the lookout for was something to turn off the
boiler if the (water) temperature overshoots it's set limit. I think this is
the thermal cutout you describe... according to the docs on baxi/partsarena,
the Medway Super had such an "energy cut-off device". For better or worse,
my model is too primative to have one of these.

*I had the case open as I wanted to remove the HX to de-scale it, long
overdue after 20 years!. I followed my new-found instructions, undid the
unions and screws, but when it came to it the flue part of the HX is
immovably fixed into the wall-mounted flue housing - it really won't budge.
So, all I can think of is wait until if/when it gets disconnected for
replumbing. Then, connect into cold in / hot out pipes and somehow run
descalant through the whole thing - flow sensors and all (do these contain a
rubber diaphram and are they the 'weakest link'?) These will also have to
survive 'Fernox' of similar, and anything else coming out of the radiators
if my mad plan actually happens.

Wonder if you can still get spares for these things?

DIYSOS