Corsa C 1.3 water leak and high pressure in cooling system

[BeneFactor]

I'm using my car for 2 hours a day. Next day I'm opening the coolant tank cap, it starts to sound "ssssss" and coolant level rises to normal level. Everyday its same. I tested my head gasket with Würth Co2-leak tester, and there is no leak, so head gasket is okay. Someone told me that EGR Cooler can cause problem like this. Btw when i start driving, depending my driving style; coolant tank cap leaks as very little drops. And my coolant color turns orange, at first it was pink. Should I change EGR cooler? Or water pump? I'm confused can you help me? Thanks a lot.


Sorry for my bad English. My car is Opel Corsa 2006 1.3 CDTI (diesel)