Zoe Anderson was killed in 2010 by carbon monoxide fumes which leaked from a boiler fitted by Andrew Hartley

A gas fitter has been found guilty of killing a 24-year-old woman who was overcome by carbon monoxide fumes from a newly-fitted boiler.

Zoe Anderson was found dead by her boyfriend in the shower room at her millionaire father's home in Bath shortly after Christmas 2010.

The Victorian townhouse had been "flooded" by the lethal fumes which leaked out of a faulty boiler flue fitted by Andrew Hartley. Bristol crown court was told Hartley, 37, did a "rushed" and "botched job" and a jury found him guilty of manslaughter by gross negligence. At first it was thought Anderson had slipped and banged her head but later it was found she had collapsed from carbon monoxide poisoning. The prosecution said Hartley, who was paid more than ?2,000, failed to secure the flue pipe correctly, if at all.

"The only person who really knows how the installation went is Mr Hartley," prosecutor James Townsend said. "Initially no one knew what had caused Zoe's death but after an examination by a pathologist it was clear she had died from carbon monoxide poisoning.

"When the boiler was working, instead of the fumes going down the piping to the outside they were being blown out into the garage." Carbon monoxide had been "pouring" into the house, he added.

Anderson had been in the US visiting her father while the boiler was fitted but returned to Bath on 27 December and complained the boiler was not working and the house was freezing. She was due to meet a friend at the cinema the next night but failed to arrive.

The next day her boyfriend, Alastair Uhlig, travelled from London to meet her but when he arrived at the house he could not get inside. He fetched a spare set of keys and found his girlfriend's body in the shower room.

Hartley, who has been in the gas and plumbing industry for 20 years and had an unblemished career, said the boiler had been correctly fitted and suggested the flue pipe had become disconnected during the cold weather.

He was said by colleagues, acquaintances and friends to be reliable, professional and trustworthy.

He said that when he left Anderson's home the Worcester boiler was working properly and he had fully tested it.

Speaking before the verdict, Judge Neil Ford QC told the jury: "Carbon monoxide is an insidious substance. You can't see it, you can't smell it. It can overcome people very quickly.

"It is for this reason Zoe was owed a duty of care." Hartley, of Radstock, Somerset, will be sentenced next month.

Writing after his daughter's death, Anderson , the founder of a magazine empire and a leading force in Ted, which aims to spread ground-breaking ideas across the globe through talks, conferences and other events, paid tribute to "my dazzling daughter".

He wrote after her death: "Two weeks ago today, riding a ski-lift on a glorious clear day in Whistler, I got the impossible phone call. Zoe, my beautiful, larger-than-life 24-year-old daughter had been found dead at our home in Bath, England.

"On Saturday we gathered in England with friends and family from all around the world to celebrate an extraordinary life.

"Amidst the terrifying grief, some light began to shine through as we marvelled at the ways her life had touched so many people."

Speaking outside court after the verdict, Ms Anderson's mother Lucy Evans, an artist, said she had found forgiveness "hard work".

"When we lost our Zoe just over a year ago we all felt an intense pain and bewilderment. No one could answer our questions as to why it had happened and it made losing her so much worse.

"We are grateful to all those who have given their time and expertise to help us find those answers. A tragedy like this can be so destructive on all sides and at times I have found forgiveness hard work.

"But the Bible promises me that the truth will set us free. So I have prayed that our hearts and minds will be set free now.

"Free to enjoy the fabulous memories we have of Zoe, free to forgive, free to nurture and help each other and to rebuild our lives."

Detective Inspector Neil Beament, who led the investigation, said: "This is a tragic, tragic case. Andrew Hartley is a professional tradesman with all the relevant qualifications.

"His substandard work has led to the death of Zoe Anderson, a young woman with a very bright future.

"The verdict reflects the severity of his failings and sends a clear message to all tradesmen in relation to the duty of care they owe all their customers.

"The case also highlights the dangers of carbon monoxide poisoning and I would urge all householders to consider the installation of appropriate devices."