leaking heater valve?

[Driller]

Went out the other morning, car completely cold and checked the expansion tank level. What happened was totally unexpected: as I loosened the blue Audi cap there was a release of pressure and some water overflowed so I quickly put the cap back. On a cold engine? Also not sure if related but have found a little patch of water on passenger side floor which appears to be coming from a leak where the pipe from the heater valve goes forward into the bulkhead.
Any offers or has anyone else had this happen?

[Leadfoot]

Leaking head gasket pressurising the cooling system? Oh err
Otherwise, have you had the cooling system apart recently & introduced a big air lock?

[Driller]

Had a new rad put in 2 weeks ago? Shit I hope it's not the head gasket. Going in for service soon so i'll find out soon enough

[Leadfoot]

air lock sounds a likely suspect to me then. Was this the first time you checked the level in the expansion tank after the new rad?

[richb]

The radiator should have a bleed valve at the top in one corner, try releasing it to see if any air comes out...

[driller]

Thanks chaps I'll give that a try. As for the leak, just remembered I had cleaned the car and I think the water was coming in around a pipe through the bulkhead-whoops...