The firefighters' union said questions had been "left unanswered" over Zane Gbangola's death at his Chertsey home.
An inquest concluded he died of carbon monoxide poisoning generated by a petrol pump used to clear floodwater.
Zane's parents believe hydrogen cyanide (HCN) from a lake built over a former landfill site killed their son.
Lee Belsten, from the Surrey FBU, which has members who dealt with the incident, said: "It is public knowledge that hydrogen cyanide was detected in the house and we'd ask that gets looked into.
"From behind the house, there was a landfill site."
He added: "We have to get the government to look at this."
He said landfill could be a source of toxic gases, but no soil or water testing at the house or the land behind it found evidence of a source of HCN.
Mr Travers also found all the family had normal HCN readings when tested.
"How anybody could suggest something different for Zane is beyond me," he said.
The family have previously criticised the conduct of the inquest claiming anything to do with HCN was "marginalised", and Andy Burnham MP described the handling of the hearing as "seriously flawed" .