Riley Holt, eight, Keegan Unitt, six, Tilly Rose Unitt, four, and Olly Unitt, age three, died in the blaze in Highfields estate last Tuesday.
After speculation online, Staffordshire Police said they had ruled out the two rumours.
Detective Inspector Alan Lyford, of Staffordshire Police, said: “This is a complex ongoing investigation and, while we appreciate there is a demand for answers, our primary aim is to understand exactly what happened in this tragic fire.”
Det Insp Lyford said that, following preliminary findings from fire investigators, he had taken the decision to rule out several rumours which had spread locally.
“We do not believe that a boiler defect was responsible and we can confirm there is no truth in rumours that cannabis was being grown at the property and may have been a cause.”
“We’d again like to thank people for their patience, but kindly ask that people do not speculate as such comments can be misleading to an investigation as well as causing upset.”
A woman, 24, and a man, 28, arrested on suspicion of manslaughter by gross negligence, have been bailed.
The woman and man are currently living at an address out of the area.
They were detained by officers on Friday and have been bailed until March.
The investigation is still ongoing.
The children's 24-year-old mother, Natalie Unitt, and her 28-year-old partner, Chris Moulton, leapt from a first-floor window with the siblings' two-year-old brother, Jack, during the fire.
They did not sustain life-threatening injuries.
A fundraising page for the family has since raised over £30,000.
Candlelit vigil held as tributes pour in
A candlelit vigil was held last week to remember the siblings killed in the fire.
Hundreds of people carried flowers, candles and tributes to the young victims.
With police closing the surrounding roads to allow the parade to head through, members of the family led the march through Sundown Drive and Milton Grove towards the police cordon on Whittingham Drive.
WATCH: Community unites in grief
The vigil took place on Thursday evening.
In the distance people can see the wreckage of the family home on Sycamore Lane that was devastated by the blaze.
Before the march began, the grandmother of the victims, who wished to not be named, fought back tears to address the crowd.
She said: "Thank you very much for coming and supporting our family.
"That's all I can say, just thank you very much."
The vigil began at The Oxleathers pub and was organised by landlady Debbie Howe.
She said: "It's just been very sad, the morning of it all and since then it's never stopped, I can't really put into words what has gone on.
"The community has been unreal, they've pulled together and Stafford and even further.
"The Just Giving page has been amazing, it's been astonishing.
"It's something that has never happened in my life, and I'm 40-years-old, it's very sad.
Stand up comedian Roy 'Chubby' Brown has also donated £700 to the family.
He was performing at The Gatehouse Theatre on Friday, three days after four children lost their lives.
Flowers left in memory of siblings
Residents in Highfield were still in shock as the number of tributes left at the road to the house continued to grow.
A bag from nearby Castlechurch Primary School, where three of the youngsters were enrolled, was placed carefully on the ground on Whittingham Drive and filled with stuffed toys.
A message from Castlechurch schoolchildren said: "Riley, I hope this day didn't happen but it did.
"Love Archie and your class."
Bunches of flowers have been left in the road with people touched by the tragic deaths.