This one has me scratching my head a little!

I have a Baumatic oven that has decided not to get as hot as it used
to. Dunno the model number (can't find it anywhere) but is a fan oven
with a top element. I also thought there would be an element around the
fan in the back of the oven but have checked and there isnt??
Anyway, have metered the top element and readings are as follows:
Outer - 56.9 ohms
Inner - 24.2 ohms

When I turn the oven on with the stat on full the element light comes
on and it starts warming up, gets to about 150 C, but never goes above
that. If you then turn the stat down you can hear it click at 150 C but
the element light stays on?

Any ideas?

Cheers

Steve