luke - thanks thermostat was perfect fit.
i understand all the doubts, agree doesnt seem to be logic in turning the heater to cold the car runs ok and doesnt overheat, only thing i have noticed when the heater was on hot and the car started to overheat there was always an air lock somewhere, either the heater would go cold and the car start to over heat, another time after driving it for 20 miles i turned the heater on it started to over heat and thats when i checked the outlet from rad and it was cold.
yes heater does run very hot when on. i am also bleeding via the correct 3 points. i will drive the car for the rest of the week with heater turned off and see, i do have my doubts and maybe you are correct, if its dry at the weekend i will do a reverse flush of the matrix, if still overheating rad removal and clean will be next.