Cylinder head gasket? Volvo 850 T5R

Good evening, I have a question regarding cylinder head gasket. My favorite is ticking something A few weeks ago I noticed that he has a cooling water loss. (The symbol started to light while driving, despite several times refilling..) In addition, there was an extraordinary amount of pressure on the container. I then checked all hoses and found a leak in the water hose from the cooler to the thermostat. Then I changed all pipes and hoses incl. Of course everything was ventilated. Then the problem had been solved. 3-4 days later the whole thing started again. Water is getting less from time to time. However, you don’t see anywhere where water or oil is. If I screw up the oil filler screw everything looks normal. ) If the car has operating temperature are d he water hoses are not exceptionally hard. Then I tried to generate pressure with a pressure pump (cooler tester) on the balance tank (0,9-1,3bar) and there was so much back pressure from the system that it threw out the device. And now the question is.. does it point to the cylinder head seal ? Or could it be something else.. Would like to be safe before I exchange everything.. I hope someone can help me.. many thanks already. Mfg Grac ia