It’s that kind of thing although mine is normally open at low temp, and
then closes once the temperature rises above a certain level.
I decided to phone Myson who think that the stat is unlikely to be the
issue. They either work or they don’t, they don’t “half fail” with poor
conductivities and they suggested that the motor speed variation is more
likely down to just the age of the motor. Apparently the stat should close
at 31C.
After this conversation I shorted out the stat and indeed the motor speed
did still wander about a bit (on the low speed setting) which fits with
what they said.
Not sure why it’s just not starting sometimes. May still be a motor issue
but to complicate things I have an external wireless room stat also
controlling the supply to the fan so I may need to delve into that.