Boeing Co. said it would return its Starliner spacecraft to a factory for “deeper-level troubleshooting” to fix stuck valves that have delayed a planned launch this summer until perhaps next year.

The decision to remove the Starliner from atop the rocket that was supposed to propel it into space is expected to delay its launch by several months. Boeing and NASA officials said Friday it was too soon to predict whether the launch—a redo of a failed attempt in 2019—would occur this year.

“We’re going to go fix this problem,” associate NASA administrator Kathy Lueders said. “The team needs some time now to really be able to figure out what’s wrong.”

Boeing said its preliminary analysis indicated that moisture in the spacecraft’s propulsion system somehow resulted in corrosion on 13, or more than half, of certain valves and prevented them from opening properly, according to John Vollmer, a company executive who oversees the Starliner.

The valves open and close to allow—or stop if needed—the flow of certain chemicals used to propel the spacecraft at various stages of the mission and are key to its safety.