A fire at a farmhouse in which a father and five of his children aged four to 11 died may have been caused by a stray ember from a log burner or by an electrical problem, an inquest has heard.

Investigators said they believed the blaze began in or near the living room of the house in mid-Wales and that it must have reached more than 1,000C.

Police said they were continuing to investigate the fire and had not ruled out that it had been started deliberately but they had found no evidence of third-party involvement.

Dave Cuthbertson, 68, died in the fire alongside his children Just Raine, 11, Reef Raine, 10, Misty Raine, nine, Patch Raine, six, and Gypsy Grey Raine, four.

Cuthbertson, a builder, was home with eight of his children when the blaze broke out at the remote Poityn Farm in Llangammarch Wells, Powys, on 30 October last year. Three of the children – Leaf, 13, Blue, 12, and Farr, 11 – managed to escape and alert neighbours.

The hearing was told that Blue woke to the sound of screams and climbed out of a window and on to the roof before running away to raise the alarm.

Reading a statement, the Powys coroner Andrew Barkley said: “[Blue] was woken in the night by someone screaming and shouting. He was coughing and couldn’t breathe very well.

“He opened a window and climbed on to the roof. After climbing down and raising the alarm he then went back to the house and looked through the living room window. He said the fire was like a star and was too bright to look at.”

His older sister Leaf said she woke up to find her bedroom above the lounge was full of smoke. Barkley said: “She could see grey smoke coming from downstairs and went into her father’s bedroom to tell him the house was on fire. She ran to the second floor and called out to her brothers who were sleeping there. She got outside and she could hear her father calling for the other children to get out.”

Firefighters were unable to enter the property due to extreme heat and risk of collapse. Roger Smith, a crew manager of the mid- and west Wales fire and rescue service, told the inquest in Welshpool: “The property was fully on fire. All the windows were blackened. On the left-hand side the windows were broken.

“There was enormous radiated heat coming from the windows. The roof had fallen through and there were signs of collapse. It was incredibly hot. You couldn’t go anywhere near the windows. We had no idea of the location of the occupants of the property. There were no signs of life.

“I heard no fire alarms at all. The fire was fully developed, so I imagine the heat in the property would have melted them.”

Richard Hancock, the manager of the fire service’s investigation team, listed a number of objects found in the ruins that could have caused the fire. He told the inquest: “We found cigarette lighters, candleholders, and quite a lot of electric wiring. Hundreds of metres of different cables with socket extension blocks. They were being so-called daisy chained [linked together], which is not the best practice in the world. Electricity does still remain a possible cause of ignition.”

But he also told the inquest: “It is possible that a spark or ember from the log burner in the room had jumped on to furnishings. There was no spark guard as such. The metal cage around the log burner served only as a child guard.

“Given the degree of destruction in the room of origin and accounts placing the fire in the ground floor lounge, it was very difficult to identify one particular item as being the cause of the fire. We found copper piping on the wall inside the property had melted. Copper melts at a temperature of 1,085C.”

Cuthbertson, who was born in Scotland, was identified through DNA, as were Just, Reef, Misty and Patch. Gypsy was identified through dental and skeletal analysis.

The children’s mother, Sima Khan, who did not live at the farmhouse, confirmed their identities, address and dates of birth.

The coroner recorded a narrative conclusion, saying each had died from inhalation of fire fumes, but there was no clear evidence what started the fire.

After the inquest, a statement from relatives of the family said: “We as a family would like to once again thank all the emergency services for the hard work and dedication throughout the past year and we thank the public for their continued support.”