Fire officers have arrived at the house in the village of Troedyrhiw, where the bodies of an adult and a child were discovered yesterday.
The Merthyr Tydfil crew were called in by South Wales Police.
Joanne Thomas and her four-month-old baby Harper were found dead at their home in Merthyr Tydfil in July. An open verdict has been recorded.
Police add there is 'no evidence to date' to suggest carbon monoxide killed the two, believed to be a mother and her four-month-old baby.