The oxygen supply system on the Zvezda module at Orbital Lab failed late on Wednesday, but a second system on the US section is operating normally, a spokesman for Roskosmos told AFP.
The spokesperson said that nothing happened threatens the safety of the crew and the ISS.
The issue arose after three new crew – two Russian Cosmonauts and one American astronaut – reached the ISS on Wednesday to bring the current crew number six on board.
The problem is the latest incident on the ISS – whose first module was launched two decades ago in 1998 – after the crew in August detected an air leak on board.
Roscosmos insisted at the time that the leak was not significant and there was no danger. But part of the problem was finding out exactly where it came from.
The crew believes they have now found the source of the leak. A spokesman for Roskosmos said they would receive precise instructions from Mission Control to carry out future work on the problem.
Referring to the RIA Novosti news agency, veteran Russian Cosmonaut Gennady Padalka stated that Russian equipment aboard the ISS was just before the date of its use.
“All modules of the Russian section are finished,” said Padalka, who holds the world record for most days spent in space.
He said the device should only be used for 15 years, while it was now two decades old.
© Agence France-Presse