Bernard Hender, 19, and Doug McTavish, 39, died in the blaze above a funeral director's office in Llanrwst, Conwy county, in October 2014.
The Abergele inquest is examining if a Hotpoint dryer caused the fire.
On Thursday, a fire engineer told the hearing there was "no compelling evidence" it started in the dryer but he could not rule it out.
Clifford Christie, a member of the Institute of Fire Engineers, was asked to look into the cause of the fire by domestic appliance company Whirlpool.
Giving evidence on the second day of the hearing, he said the dryer was "severely damaged" by fire but some components on the machine were intact.
Mr Christie said he was "satisfied" it had not started in the timer, the motor or the drum, and there was no accumulation of lint in the machine.
But he said he could not rule out that it started in the machine's starter switch, which was not recovered following the blaze.
He also told the hearing it was possible there was a fault in an iron kept in the same room.
He said evidence given to the inquest on Wednesday that the iron was switched off might have been "mistaken".
On Wednesday, a tenant who lived in the flat spoke of surviving the fire.
Garry Lloyd Jones, 50, told the inquest: "I just remember walking down the corridor to see what was going on and seeing flames coming out of the tumble dryer.
"I went down to the living area and went to the kitchen and there was nothing there but when I looked out of the kitchen window I could see an orange glow."
Notices had previously been issued by Whirlpool telling customers to unplug Hotpoint, Creda and Indesit models manufactured between 2004 and 2015 after a potential fire risk was identified.
The inquest continues.
A tumble dryer could "not be ruled out" as the cause of a flat fire in which two men died, an inquest has heard.