Billy Johns was four years old and one of seven children living with his mother, Ms Kovacs, in their McMenamin Place property when it was engulfed in flames on September 15, 2010.

Ms Kovacs and six of her children, aged between seven weeks and 15, escaped the fire, but Billy was not with them.

Police at the scene tried to force their way into the house, but were driven back by the smoke and flames. Firefighters found Billy lying at the foot of his bed.

He was unable to be resuscitated and was pronounced dead at Bathurst Base Hospital.

Police investigating the fire at the time quashed a theory it was started by a Molotov cocktail thrown through the window, but Ms Kovacs disagrees, saying she knows what she saw.

Since Billy’s death, Ms Kovacs has fought for an inquest into the tragedy, but said her requests have been denied.

In a letter written to Ms Kovacs, NSW State Coroner Michael Barnes said he had reviewed the application for an inquest, but had come to the conclusion the fatal fire "was not lit by anybody external to the house”.

He said forensic evidence indicated the broken windows at the front of the house were in some cases already broken and in other cases shattered as a result of the heat generated by the fire.

Mr Barnes said there was no evidence indicating anything had been thrown through any of the windows causing them to break at the time the fire broke out.

He said phone records for the person Ms Kovacs suspected of being involved in lighting the fire showed he was at home at the time, and the person implicating him in the fire was not a reliable witness.

Mr Barnes also stated there was "ample evidence" Billy had access to matches or a lighter and was in the habit of lighting fires when unsupervised.

Mr Barnes there was no basis on which he could conclude the decision to dispense with an inquest could be overturned, and Ms Kovacs’ application was denied.