A faulty valve on a gas line at recently renovated Stratfield Elementary School is blamed as the cause of a gas odor that forced evacuation of the school Tuesday.

Meanwhile, tests by firefighters dispatched to the school indicated there also was an elevated level of carbon monoxide in the boiler equipment, but officials indicated it posed no health risk since it was detected only within a chimney.

Evacuation of students and staff was ordered as a safety precaution about 2:30 p.m. after the smell was detected at the Melville Avenue school.

Tom Cullen, the school district's director of operations, said the Fire Department and a certified plumber from a town-owned maintenance shop were notified of the odor.

The district's central office was then informed of a possible gas leak, soon after which Dave Fryer, manager of facilities, and Mike Priatt, maintenance supervisor, were sent to the school with the plumber, Cullen said. They discovered the odor was emanating from the boiler room installed during the school's recent renovation. The origin of the odor was a faulty valve on the gas line in the boiler room, he said.

There was no leak of gas detected inside the building, but an elevated level of carbon monoxide was found within the boiler's chimney, said Assistant Fire Chief Scott Bisson, the shift commander who was at the school Tuesday.

"Children were not at risk," he said. "Upon investigation, it was determined there was a problem with the operation of the boiler."

Firefighters allowed students and staff back into the school by 2:50 p.m., Cullen said.