Well the title is probably wrong but I couldn't think of anything else
)

My problem is that although I think the thermostat works (water doesn't
boil) even if I set it to it's lowest temperature the water still gets
very hot, I estimate around 60 degrees, certainly enough to scald.

I am beginning to wonder if the problem is that the stat rod seems a
very loose fit in the pocket tube (terminology?) and I am wondering if
it just isn't making good enough contact to warm up enough to turn off
at the right temp. I asked in a plumbers merchant if there were
different diameter stats and I was told there all the same, is this
true.

Lastly can you put some sort of oil in the tube to make good thermal
contact with the stst or something?

Any help gratefully received.