PARKS, Ariz. — A contractor has found a “significant failure” in the heating system at an Arizona vacation cabin where a family of four was found dead of possible carbon monoxide poisoning, authorities said Tuesday.

Coconino County sheriff’s officials said the heating unit was the only gas appliance in the cabin in Parks, about 20 miles west of Flagstaff.

In a statement, sheriff’s officials said a licensed contractor from a heating and cooling company checked the unit at the cabin and “found a significant failure in the heating system which would be consistent with carbon monoxide overcoming the residence.”

Sheriff’s officials added that the manner and cause of death will be determined by the county Medical Examiner’s Office.

The bodies of the four family members, including two children, were discovered Monday following a request for a welfare check.

A friend of the family told deputies that members had not returned phone calls.

Authorities said a deputy reported a strong odor of gas coming from the home before the bodies were discovered.

The El Mirage family has been identified as 32-year-old Anthony Capitano, 32-year-old Meaghan Capitano, 4-year-old Lincoln Capitano and 3-year-old Kingsley Capitano.

El Mirage is located about 25 miles northwest of Phoenix.