A Saint John family says they’re lucky to be alive after a faulty heating system left a babysitter and two children with carbon monoxide poisoning.

Jessica Sypher says she returned to her Crown Street home Friday night to find the babysitter incoherent.

“He came downstairs and he was shaking,” says Gean Sypher, Jessica’s mother. “Walking down the stairs he said, ‘I don't know what to do,’ and it kind of looked like he was going to faint."

Gean Sypher then ran to check on the two small children.

“I went into the living room to check on the kids and they were sleeping. Really sleeping. They were unconscious, on their way out," she says.

The two children and their babysitter were all airlifted to hospitals in Halifax, where they were successfully treated and released.

As part of their investigation, the Saint John Fire Department has seized the boiler from the building's heating system..

"Carbon monoxide is a silent killer,” says Mark Wilson, Chief of the Saint John Fire Department. “It's odourless, tasteless. You can't see it until, in a lot of cases like you're in a confined space like an apartment, until it’s too late."

New Brunswick housing authorities tell CTV News, "All NB Housing units that have natural gas heating systems have carbon monoxide alarms and all boilers are inspected annually."

It appears the carbon monoxide detector was working at the time. Jessica Sypher says she heard it when she got in the door.

"It sounded like a smoke detector battery dying. It was just like a beep, beep, over and over again,” she says.

Additional alarms have now been installed in two of the townhouse units, including the Sypher home. But the family is haunted by events of the past weekend and wants to move out.

"I don't want to be in a place with a furnace. Too scared now," Jessica Sypher says.

"I wouldn't live here either,” says her mother. “I can close my eyes right now and see everything that happened that night."

This was this family's first encounter with carbon monoxide. They say they had no idea about the dangers of carbon monoxide before this incident.

Housing authorities say all of the boilers in the neighbourhood are being re-inspected this week just in case.

With files from CTV Atlantic’s Mike Cameron.