SAN FRANCISCO (BCN) – A San Francisco Indian restaurant has resumed meal service not more than a day after it was shut down for a carbon monoxide leak that hospitalized several people, according to the restaurant manager.

Four guests at the neighboring Marriott Marquis fell ill Thursday night after a water heater in Amber India at 25 Yerba Buena Lane leaked high amounts of carbon monoxide into the hotel walls, according to the San Francisco Fire Department.

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The problem was tracked to a “strange-looking” pipe connected to the heater and eventually it was shut down on Friday, but the restaurant managed to install a temporary heater and began serving customers Saturday night.

“We couldn’t shut down the restaurant,” Maneesh Rawat, general manager of the restaurant said.

The replacement heater is operated on electricity only and meant as a temporary solution, he said.

“We can’t use it permanently because it’s too expensive and not eco-friendly,” he said.

The broken heater—which uses both electricity and gas—began malfunctioning near Christmas and wouldn’t warm up water because of what was believed to be an electrical issue.

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The restaurant had work done on the faulty appliance and turned it back on, which is when the hotel guests became sick.

On the night of the incident, Amber India’s venting system was leaking carbon monoxide into a shaft between walls in the hotel. Normal carbon monoxide levels are about 25 parts per million, but readings in the hotel were well over 250 parts per million, according to officials.

The guests were flight attendants staying in four separate rooms at the hotel, which is at the intersection of Fourth and Mission streets.

At about 10:40 p.m., the guests complained of flu-like symptoms, and the hotel’s doctor was contacted.

The guests were transported to San Francisco General Hospital and St. Francis Memorial Hospital, where they were doing well since Friday morning, hotel spokesman Sam Singer said.

No claims have been filed against the restaurant, Rawat said, but he expects an investigation into the issue will be ongoing.

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“There’s nothing we have done from our side that is right or wrong,” he said. “That water heater was installed 3 years ago, and nothing has been changed since then.”