A replacement Interislander ferry that broke down on Friday cancelling two crossings between Wellington and Picton is back in service for the 5pm sailing.
A faulty valve in a cooling system is being blamed for causing an electrical failure which affected a propeller.
The Stena Alegra, from Poland, went into operation on Monday after extensive test sailings. It is being used to temporarily replace the ferry Aratere which lost a propeller on 5 November, midway through a crossing from Picton to Wellington.
InterIslander general manager Thomas Davis said the Stena Alegra left berth about 4.30am on Friday but there was an issue with the engines and a partial power failure.
The ferry was being used between Poland and Sweden before it ran aground in a storm. Interislander general manager Thomas Davis said the grounding and Friday's fault aren't linked.
The early freight-only sailing and the return passenger crossing from Picton at 9am were cancelled. Mr Davis says 148 vehicles were booked on the later sailing and almost all have been rebooked on another crossing.
Michael Roberts manages refrigerated food freight company Big Chill Distribution. He said delays are costly to a company dealing with perishables, and it lost tens of thousands of dollars a month when Interislander wasn't at full capacity.
Interislander on Friday apologised for inconvenience caused to customers and passengers.