Hi. My zafira has been steaming and losing coolant. I've noticed (although might be a coincidence) that it only steams when the heating system is on. The garage have said its the head gasket but I'm not entirely convinced as there is no other symptoms etc. I spoke to a vauxhall specialist who said often when the oil cooler or seals need replacing that it's misdiagnosed with head gasket. Does anyone have any idea what could be causing this issue? Or is it probably the head gasket. I ordered a new oil cooler to try that but I'm near at my wits end here. Thanks 

Thats an odd one!

Looking at the videos it seems to be emanating from around the exhaust manifold area.
I would run a coolant pressure check to determine if there is pressure loss with the heater on and then off.
Also, a pressure test would show exactly where the leak is (even if it is in the cylinders it would show in the exhaust - white smoke)