could you take out the temp sensor and put it in boiling water (may have to add some wire to reach) to see if gauge works then?
also can your garage do a sniff test on the rad while bubbles are coming up? - that will show if head gasket is leaking.
also, i had a car once that used to leak water and when it was below temp sensor the gauge would read cold so it could be air pocket around sensor as stated above?

thats fine
please pm me your details
thanks

just posting to say hi
just got a slightly faulty fazer 1000 gen 1 so i thought i would join up for tips and advice while i try and get it sorted