[jb92563]

I read on this forum that a coolant flush at a shop should be done with the negative pressure equipment in order to get the bubbles out.

If you try to do it with the burp valve open you may need to run it that way for a week and of course water will come out occasionally in the process.

Also, if they filled the coolant tank to the top line when cold its likely to expel some coolant. Overfilled
I don't go more than half way between fill and full marks on the tank when its cold.

Statistically a head leak is unlikely as its not very common occurance.

Other worse things like the D Chunk blowout will show up as water in your oil or oil in your water.

Another possibility is that the burp valve has some loose screws or lost its gasket, but if you are driving with it open, then its possible some water will escape through it.

Its also quite easy to screw the coolant cap on wrong so I would take some extra care to make sure its on properly and level.