So further to a 3 year battle with coolant issues finally got to the bottom of the problem. Combination of charge cooler, egr cooler , silicone bag in the header tank, and heater matrix. For anyone expericing coolant loss or header tank pressure dont confuse this to be a headgasket fault. Do your checks first

I have a coolant loss.

Changed the water pump and regulator 3 weeks ago and still loosing coolant.