OK So as I previously mentioned the heater the Fiesta I just bought is temperamental, anyway today I had the bonnet open and to my surprise the tank was empty. I looked inside and there was just enough water in there so that it filled the pipes.Now it seems odd that the previous owner had not picked up on this, or the garage who inspected the car. Either the coolant has been neglected way too long or there a serious leak.

I just put some water in there from the water filter in the kitchen and drove the super market and bought a bottle of universal 5 year anti freeze and some deionised water. I put in about half the 1lr bottle of anti freeze and added some deionsed water until it was to the max. And then I had to do some urban waiting in traffic and going up hills for about 15 minutes and by the time I got there the water was very hot and very orange.
This panicked me at first but as far as I could tell it was from rust specs, there does not appear to be any oil in the water or water in the oil, the oil in fact looks immaculate, no "mayonnaise".
Should I just do a flush and add fresh anti freeze and add Radweld?