I've just done a rebuild of my head.
the overheating light is constantly on. I have checked water, oil, compression, everything! I'm thinking when everything was put back together, I may have knocked the sensor?
any ideas?

 

I think you are referring to the 'low coolant' warning light.

The sensor is in the brown coolant header tank. Most likely the wire has come off.

Cheers
DD

 

thanks mate. I have a feeling it's something like that. There's no sign of overheating and the coolant is still full.