Thanks for your replies to this
Chrishutt i have done what you suggested and looked in the FAQ and i only found this to relate to my problem
"Feed and Expansion tank
Open vented systems are filled and vented to a Feed & Expansion (F&E) tank. This is usually a small plastic tank in the...
What i think is the Radiator overflow is doing its job right by returning the excess water to the radiator header tank (water in header tank is warm can see steam coming from it).
With the water being returned the header tank now contains too much water and is now coming out of the overflow...