The Waterloo Fire Department responded shortly before 10 p.m. Thursday to Gardner Elementary School for the report of a haze in the building and a smell of smoke.

Three maintenance workers inside the school were evacuated as a precaution.

Fire officials on scene confirmed a burning smell while on scene but could not detect any obvious indication of a fire. Firefighters conducted a thorough investigation inside and on the roof of the school located at 1 Ed Gardner Place off East Fourth Street.

Shortly after 10:30 p.m., a fire official reported that the source of the burning smell was located in one of the restrooms of the school.

The WFD cleared the scene shortly after 10:50 p.m.

Waterloo Superintendent of Schools Brian Charron said firefighters found an electric hot water circulation pump that failed and tripped the breaker.

“I’m told it was still hot when they found it,” Charron said.

This pump delivers hot water to restrooms so students have warm water for handwashing. Charron said that until this pump is replaced, students at Gardner will only have cold water for handwashing.

Waterloo Fire Chief Mike Lloyd confirmed what Charron offered as an explanation for the fire call.

“Power was shut off to the pump,” Lloyd said. “We ventilated a couple of hallways and classrooms.”

Lloyd stressed that the Thursday night call “was not related to any previous calls we have had there.”

The WFD joined police and EMS in responding to Gardner last Friday morning after multiple students reported feeling ill during play practice in the gym.