luddite

Hello every one i have trawled through the net trying to sort out my issue can any one help
Here goes eng coolant overflows with no fan action
have checked:
coolant cap
changed thermostat assy including tempsensor
removed temp sensor connection fan does not come on
proved fan works by connecting to battery
fuses checked ok
ecu shows p0118 coolant temp sensor 1circuit high with amber eng warning
so could it be the relay if so where is it situated? (behind fuse box but which one?)
or thermister at bottom l/h side of radiator?


If you have no idears could anyone recommend a reputable electrical car technician in the chessington surrey area.

thanks