Two men and a woman died on Tuesday night at their home in Carrión de los Condes, Palencia, as a result of carbon monoxide poisoning.
The incident occurred at around 22:00 on Tuesday and the victims were a couple, aged 40 years and 50 years, and the 70 year old father of the woman.
It is thought that the situation was caused either by the two chimneys in the house or the boiler.