Bristol plumber Andrew Hartley has been found guilty of manslaughter after a 'botched' flue installation which led to the death of Zoë Anderson from carbon monoxide poisoning.

Hartley fitted the new boiler into Anderson's home in Bath less than two weeks before gas fumes overcame her.

The 37-year-old plumber had already admitted a charge of breaching gas safety regulations by failing to secure the boiler flue pipe with screws, but a jury at Bristol Crown Court this week found Hartley guilty of manslaughter by gross negligence following his work on the appliance in December 2010.

During the trial the prosecution said Hartley – who was paid more than £2,000 – did a 'rushed' and 'botched' job, failing to secure the flue pipe correctly, if at all.

Anderson died within 30 minutes of being exposed to the carbon monoxide after fumes leaked from the flue pipe connected to the boiler in the garage of her Victorian townhouse. When the boiler was working, instead of the fumes going down the flue pipe to the outside, they were being blown out into the garage.

Prosecutor James Townsend told jurors: "The extension pipe should be firmly fitted to the turret flue elbow and in addition the extension piping should be secured in the turret elbow with the use of screws. The only explanation for the boiler leaking the fumes within days of the fitting can be that it wasn't attached at all in the first place or if it was, it wasn't left fitted correctly."

Hartley was arrested on suspicion of manslaughter and admitted he had neglected to fit screws to the extension pipe but maintained the boiler had been correctly fitted. He suggested the flue pipe had become disconnected during the cold weather.

Townsend said: "The failure to fit the screws, a tiny but important job in its own right, was a serious measure of indication of the defendant's attitude to the job."

Colleagues said that Hartley, who has been in the gas and plumbing industry for 20 years and had an unblemished career, was reliable, professional and trustworthy.

He told jurors that he admitted a charge of contravening gas safety regulations, which reflected his failure to secure the flue pipe with screws. However, he denied he was grossly negligent and said he felt "awful" about not carrying out the installation properly.

Hartley is due to be sentenced in April.