You may have hit the nail on the head Tony, I did check for 'in'+'out' but it wasn't stamped on the valve however the vehicle came to us from another garage who had already poked about and replaced a flap position sensor so could well have put pipes back wrong.

Thinking about it now it makes perfect sense that if the pipes were interchanged in this manner it would cause this exact fault! Will let you know tomorrow.

Sometimes you can't see the woods for the trees!

Regards

Luke Browne