As Mr Peake climbed out of the space station, American astronaut Scott Kelly positioned a camera from inside so that the British flag on the arm of Mr Peake's spacesuit was visible to viewers watching live on NASA television.
Nevertheless, the incident echoed a scary episode in 2013 when Italian astronaut Luca Parmitano almost drowned inside his spacesuit.
Peake and Kopra were back inside the pressurized space station at 12:31 p.m. ET, NASA said.
Briton Tim Peake's spacewalk has ended after a water bubble was reported in the helmet of his fellow astronaut. Engineers are already looking at data to find what may have prompted the water to form inside Kopra's helmet. He said later that the water bubble was 4 inches long and getting bigger.
Kopra reported that the water in his helmet was cold, and Navias said that was a clue that the leak had something to do with the water-circulating cooling loop inside the suit. It turns out Kopra was wearing the same spacesuit involved in the earlier incident.So far, Im OK, Kopra assured everyone.
While the spacewalk was cut short, the main mission was actually accomplished.
Parmitano's partner that day, astronaut Chris Cassidy, rushed to Mission Control today after hearing of the setback to offer assistance.
Keeping in mind another spacewalker's close call in 2013, Mission Control terminated the planned six-hour spacewalk at the four-hour mark.
While Peake became the first astronaut to walk in space as a British astronaut, Michael Foale - a dual USA and British citizen - was the first person born in Britain to walk in space in 1995.
Mr Kelly said: "The Union Jack has explored all over the world, now it's exploring space".
He carried the unit, which would weigh 200 pounds (90 kilograms) on Earth, to the far end of the space station s truss, about 200 feet (60 meters) from the exit. Replacing the voltage regulator requires careful coordination - and Peak and Kopra will be working against the clock. The station has been operating smoothly with its remaining seven power channels, but NASA was concerned a second failure could be a problem.
As the ISS orbits our planet every 90 minutes, the astronauts were operating in incredibly complex conditions.
Mr Peake said he felt "exhilarated" about his upcoming spacewalk but had "no time to dwell on these emotions". Former Beatle Paul McCartney said via Twitter.