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DENVER — Over 400 people die every year in the United States from unintentional exposure to poisonous carbon monoxide gas fumes.

Many of those deaths result from faulty gas furnaces and that is why it is so important to make sure your furnace is working properly.

But, a FOX31 Denver undercover investigation found that some of Xcel Energy’s inspectors have overlooked cracks in furnaces which could potentially leak deadly gas.

Xcel HomeSmart customer Marion Williams pays $56 dollars a month extra on her utility bill for Xcel Energy’s HomeSmart service. But Williams is questioning their service. Williams said, “Three of us could have lost our lives.”

Under the HomeSmart plan, appliance maintenance, like furnace maintenance, and most repairs are free.

HomeSmart from Xcel inspected Williams’ furnace and air conditioner during the summer. Williams said the Xcel tech told her the air conditioner needed Freon, but it was not covered by her HomeSmart plan.

Williams’ grandson called another company for a second opinion. A Plumbline Services technician found a crack in the furnace heat exchanger and told Williams her furnace was unsafe. The heat exchanger vents the gasses that are produced from the furnace’s flame. If there is a crack in the heat exchanger, there is the potential for gases, including carbon monoxide, to leak in a home.

Williams said, “He wanted to know who was in the house and I told him and he said me and the two babies was in danger.” Williams contacted Xcel again and asked them to re-inspect her furnace, but once again Xcel’s worker found no visible cracks. “He said there wasn’t nothing wrong with it. He could find nothing,” she said.

Plumbline Services was concerned for Williams’ safety, so a third company, nationally recognized Heat Exchanger Experts was called.

Russell Prach from Heat Exchanger Experts said, “You can see the crack right here.”   Prach found six cracks, all visible to the naked eye and our cameras in Williams’ heat exchanger. Prach said, “It has the potential to put off carbon monoxide at any time. So it’s a very dangerous furnace. It shouldn’t be running whatsoever. “

FOX31 Denver wanted to know if Xcel’s technicians are missing cracks in furnaces so we rigged three metro homes with hidden cameras and called Xcel Energy to inspect the furnaces for cracks.

The Heat Exchanger Experts found homes with potentially dangerous furnaces. At the first home near the University of Denver, Prach showed us four cracks in the heat exchanger. Prach said, “There’s a little crack on the side here. It’s a very unsafe furnace.”

When Xcel arrived a few hours later, the technician said he tested for carbon monoxide and told our producer, “I didn’t find any cracks in the heat exchanger.” He certified the furnace to be in good working order.

At a second home in Aurora, Prach discovered three cracks. “It’s a cracked furnace and makes it a very dangerous furnace,” he said.

A HomeSmart Xcel technician then spent more than an hour inspecting the furnace and did not find any cracks. FOX31 Denver’s undercover producer asked Xcel’s technician if this meant everything was safe. Xcel’s technician said, “Yep. Yes Ma’am, it sure does.”

At a third home in Denver, Prach identified two small cracks. Prach said, “That tiny little crack, fire can shoot out of (it).”   Once again, Xcel’s technician put it in writing and then told our producer, “There are no cracks that we can see.”

FOX31 Denver wanted to know why Xcel’s technicians were not finding cracks so we showed our video to their supervisor.

Michael Montoya said, “What I’d like to say is, here at HomeSmart we are very concerned about customer safety and the first thing we do is look for cracks in the heat exchanger.”

Montoya verified he saw the cracks, but could not say why his technicians did not.   Montoya did say his technicians tested for carbon monoxide and found none.

Montoya said, “We did not find carbon monoxide, so no I don’t think those were dangerous at the time of the inspection.”

But, Montoya admits the furnaces could become dangerous. “At any time, it could yes, start leaking carbon monoxide,” Montoya said.

He insists his technicians have been trained properly, but said our video could serve as a teaching tool in the future. “Everything is a learning experience and if for some reason we overlooked something that should have been caught, we are not opposed to learning. We are not opposed to making ourselves better.”

We started investigating Xcel Energy’s inspections after we received a tip from Ellis Prach who used to train Xcel’s technicians. Prach said that Xcel’s HomeSmart service techs are not being trained properly and that their lack of training is putting customers at risk.

Denver County law requires all homes have carbon monoxide detectors. Firefighters recommend that you place a second detector by your furnace and replace all CO detectors every three years.