Nasa is looking into a problem with a malfunctioning cooling pump on the International Space Station.
The problem might eventually be serious, but there is no immediate danger to the six crew on board, according to Nasa spokesman Kelly Humphries.
The faulty external pump stopped working but is now up and running again, Mr Humphries said. It is part of one of two cooling systems aboard the orbital outpost.
He said that as a precaution, the three Russian crew members, two Americans and one Japanese shut down some minor operating systems to reduce the power load.
Engineers are trying to figure out if it is a hardware or software problem.
A valve on the malfunctioning pump shut down because it was too cool, Nasa spokesman Bob Jacobs said.
Engineers suspect a valve inside the pump was faulty and ground controllers moved electrical power supplies to the other cooling loop, Mr Jacobs said. These loops circulate ammonia outside the station to keep equipment inside and outside cool.
"The station wasn't ever in any danger," he added.
Mr Jacobs said the crew were preparing to go to bed as normal while engineers on the ground tried to troubleshoot the problem. The faulty pump and cooling loop did start up again, he said.
Mr Humphries said it was too early to speculate whether a spacewalk would be needed to fix the problem.
The station commander is cosmonaut Oleg Kotov. Americans Rick Mastracchio and Michael Hopkins, Russians Mikhail Tyurin and Sergey Ryazanaskiy, and Japanese astronaut Koichi Wakata are aboard.
The orbital outpost, the size of a football field and weighing nearly a million pounds, has been in orbit more than 220 miles above Earth since 1998.