The pump module on one of the space station's two external cooling loops automatically shut down when it reached pre-set temperature limits earlier Wednesday, the space agency reported.
Controllers on the ground moved certain electrical systems over to the second cooling loop, and some non-critical systems have been powered down inside the station, it said.
The three Russians, two Americans and one Japanese crew members aboard shut down some minor operating systems to reduce the power load while engineers are trying to figure out if this is hardware or software problem.
Initial troubleshooting suggests a flow control valve inside the pump module might not be functioning properly, NASA said.
The space agency said the "ISS can stay in current configuration" until engineers can determine a fix, even if that takes a week or two.
"You can't put a timeline on it," Josh Byerly, NASA spokesperson at the Johnson Space Center in Houston, said.