The reason the temp sensor was not working is that the bigger bit at the end that does the sensing had fallen off! Doh.
New sensor from CBS looks a lot better. The switch has an override setting so if the sensor goes you can wind it all the way up and the fan comes on even when the engine is cold.
This is the new sensor: http://www.cbsonline.co.uk/adjustabl…stat-763-p.asp
Been for a 15 mile round trip an all is well again.
The Rad is a bit border line -situation is the temp comes up and keep going up until the fan kicks in when your stopped. The fan stops the temp going further but the rad is not big enough for the temp to come back down again to normal when sat in traffic.
So it will be OK for now, We’ll see what it does when the outside temp goes up.