Jack Sheldon’s badly burnt body was found in a shed at his home on Byron Avenue, Campsall, South Yorkshire, by firefighters who were unaware that anyone was inside.
Coroner Nicola Mundy said she had concerns about fire service systems after a four-minute delay was caused by sending the wrong fire engine to the scene.
Ms Mundy told Doncaster Coroner’s Court that neighbours became aware of the fire on October 27 when they saw “a large volume of dense and dark billowing smoke”.
The inquest heard evidence from a number of people who made “valiant efforts” to put out the fire with bowls of water, fire extinguishers and hosepipes.
But Ms Mundy said: “I do believe that, at this time, this was a fully developed fire and, sadly, it’s likely that Jack had already passed away at this time due to the intensity of the fire.
“It had been thought Jack was not in the shed but it quickly became apparent Jack had been in the shed throughout.”
Ms Mundy described how Jack and his friend used a candle for light as they stripped paint from the mini motorbike using rags and petrol, which was leaking on to the table, floor and carpet.
Jack’s friend left and the inquest heard that fumes, which were likely to have built up in the shed, ignited a short time later.
Recording a verdict of accidental death, Ms Mundy said Jack passed away owing to the inhalation of the toxic fumes and the “rapid progression” of the fire.
She said: “I feel quite satisfied that Jack would have instantly lost consciousness because of the toxic effect of those fumes and would have been unaware of what was happening from that point on.
“I believe the fire was likely due to the vapour fumes in the shed. These became mixed with the oxygen such that the candle then was responsible then for igniting those fumes.”
The inquest heard that the force control room had received multiple calls regarding the fire and the nearest fire engine was not sent to the incident owing to an “error” when the calls were logged.
Ms Mundy said she did not think the resulting potential four-minute delay had altered the outcome.
But she said she has concerns about South Yorkshire Fire and Rescue Service’s systems that “could make a difference between life and death”.
She said: “While I do not think it would make any difference for Jack, such a delay could make all the difference to others should it occur again.”
Ms Mundy said she would write to the fire service about concerns regarding the systems used to send the correct appliances to incidents.