Nasa has decided that the two astronauts currently stuck on the International Space Station will return next February on a SpaceX-crewed Dragon flight where two seats have been made available for Sunita “Suni” Williams and Barry “Butch” Wilmore.

The astronauts will not return on the craft that brought them to the space station, Boeing’s Starliner, which has had problems after the capsule sprang small leaks and some of its thrusters failed.

The space agency’s announcement comes after an “agency-level review” on Saturday that included Bill Nelson, the agency administrator.

“Nasa has decided that Butch and Suni will return with [SpaceX’s] Crew-9 next February, and that Starliner will return uncrewed,” Nelson said in a press conference on Saturday.

“I want you to know that Boeing has worked very hard with Nasa to get the necessary data to make this decision. We want to further understand the root causes and understand the design improvements so that the Boeing Starliner will serve as an important part of our assured crew access to the ISS,” he added.

“Space flight is risky, even at its safest and even at its most routine, and a test flight by nature is neither safe nor routine, and so the decision to keep Butch and Suni aboard the International Space Station and bring the Boeing Starliner home uncrewed is a result of a commitment to safety,” Nelson continued.

Williams and Wilmore, two veteran astronauts, arrived at the ISS on 6 June as part of a crucial test by Starliner before it can receive Nasa approval for routine flights. However, the planned eight-day mission turned into a months-long stay for Williams and Wilmore after technical issues emerged, including reaction control thrusters that failed during Starliner’s first docking attempt.

Four of the spacecraft’s five failed thrusters have since reactivated in orbit, the Associated Press reports, adding that the thrusters are crucial for the spacecraft to back away from the ISS after undocking and for maintaining the capsule in proper position for the deorbit.

On 2 August, Boeing said in a blog post that it had conducted “extensive testing of its propulsion system in space and on the ground”. The embattled manufacturer, which has struggled to compete with SpaceX and has taken in $1.6bn in losses on the Starliner program, added: “The testing has confirmed 27 of 28 RCS [reaction control system] thrusters are healthy and back to full operational capability. Starliner’s propulsion system also maintains redundancy and the helium levels remain stable.”

In a press conference earlier this month, Ken Bowersox, associate administrator of Nasa’s space operations mission directorate, said the astronauts are doing well in space.

“Butch and Suni are well-engaged on the space station. It’s great to be there, enjoying the environment, eating that great space food and being able to look out the window,” he said.