Washington - Nasa said on Wednesday it was looking into a problem with a malfunctioning cooling pump on the International Space Station, but there was no immediate danger to the two American astronauts, three Russian cosmonauts, and Japanese astronaut on board.A valve on a pump on one of the station's two external cooling loops shut down because it was too cool Wednesday on afternoon, Nasa spokesperson Bob Jacobs said. He said that at no time was the crew at risk. But some non-critical equipment on the massive orbital outpost was powered down."It could be a serious problem, but it's not an emergency," Johnson Space Centre spokesperson Kelly Humphries said.Engineers suspect a valve inside the pump was faulty and ground controllers moved electrical power supplies to the other cooling loop, Jacobs said. These loops circulate ammonia outside the station to keep equipment inside and outside cool."The station wasn't ever in any danger," Jacobs said.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.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 450 000kg, has been in orbit more than 354km above Earth since 1998.