Hi
Thank you for your suggestions I found a small voltmeters module
The fan only has two wires ,This is connected into a fan controller module with a maximum power set to 7.5 DC , (nnormal voltage level should be 12 V, but it works fine at 7.5 DC)
Temperature reading 16.2c = 3.92 v Fan voltage
15.0c = 3.85v
14.0c = 3.74v
11.0 c= 359v
10.oc = 3.52v
Ice Block on the fan speed temperature Sensor Lowest speed min 3.20v max hot water 7v
mick