SPRINGFIELD, Mo. (AP) — Relatives of a Springfield couple who died of carbon monoxide poison allege in a lawsuit that an improperly installed water heater is to blame.

The Springfield News-Leader reports that the sons of Dwaine and Judith Crigger filed a wrongful death lawsuit last week against DeLong Plumbing Heating and Air Conditioning. The Criggers were both 70 when they were found dead in July in their home.

The lawsuit says DeLong was “negligent and/or reckless” when it installed the hot water heater in 2000 and then serviced the appliance over the next 16 years. The suit says flue gas from the appliance was the source of the carbon monoxide that killed the couple.

The attorney for the plumbing company didn’t immediately return phone calls from the News-Leader seeking comment.