Freelander S 1800 petrol

[Cornishmike]

We have a freelander S 1800 petrol 2002. A couple weeks ago we broke down losing power and then stopped, call out the aa and was told that the head gasket had gone, told he we only had it a week and I said that I had checked the oil cap to see if it was milky but he said that because it was pressurized you would see it, it was only running on three cylinders as well so we had it towed back, just had the head taken off and skimmed and pressure test new head gasket although the one that came off looked fine new modified one all put back together started up fine but seem to have to much pressure so have put the tester on the radiator reserve and it bubbles straightaway and turns the tester from blue to yellow so have carbine monoxide getting into the system somewhere any ideas what is causing this, we are going to have the head taken off again and get it pressure test by someone else just in case, don't really want to replace engine it has only done 90000 miles.