Zane Gbangbola, from Chertsey, died in hospital in February after suffering cardiac arrest.
Surrey Police are conducting tests on a petrol-driven pump that was seized from the home at the time of his death.
The family’s lawyers welcomed the report but said many questions remained unanswered.
Vijay Ganapathy, from law firm Leigh Day, said other agencies were still investigating “what toxins were present within the property on the night of Zane’s death”.
They had previously blamed an “apparent chemical poisoning” possibly caused by contaminated flood water.
An initial post-mortem examination on the seven-year-old had found “no clear cause of death” and further tests were carried out.
An inquest will be carried out by the Surrey coroner.
Police have met with Zane’s parents to update them on the findings.
They also said inquiries are being made about whether the hire company who provided the pump would face any liability or criminal offences.
The Gbangbolas’ home in Thameside was flooded for weeks in January and February when the River Thames burst its banks.
Zane and his parents were taken to hospital on 8 February after being taken ill.
His father Kye remains paralysed from the waist down following the incident.