Possible head gasket woe

[amancalledrob]

I've got a Ford Puma engine in my Fiesta and the head gasket went back in about October. I paid a garage £550 to repair and it seemed they'd done a good job until a week ago when I had exactly the same symptoms again - misfiring, wouldn't idle and clouds of coolant coming out of the exhaust pipe.

I've taken the car back to them and the thermostat's gone (failed closed which is unusual) and they say this could have led to the above. Any input on this? I wouldn't expect a failed thermostat to put coolant in the exhaust unless the coolant's boiled in the head and warped it?

[Little Pete]

Isn't the repair under warranty?

[amancalledrob]

It should be, but not if a subsequent and unforeseeable problem has caused it to go again as that wouldn't be the mechanic's fault