Sounds like you ringlands on pot 1 have give up mine did I similar thing recently and I ended up needing 2 pistons. You will need to get the head off and find out what numbers on the piston (mine were No.2) You can get pistons from camskill and you'll need a headgasket and some sump sealer. Mine cost me £65 to fix because I had spare pistons that also included a service timing belt and headgasket. And a few hour of work.