British Gas may face criminal charges after a woman died from carbon monoxide poisoning caused by a faulty boiler.
Angela Pinkney, 35, of Littlemore, Oxford, was so worried about her boiler she called out engineers several times, including on the day before she died.
The Health and Safety Executive (HSE) said it was investigating whether there was scope for bringing criminal charges under health and safety legislation.
On Thursday, an inquest jury returned a verdict of death by misadventure.
The inquest at Oxford's Old Assizes heard that the British Gas engineers left Ms Pinkney's boiler leaking carbon monoxide gas into her flat.
The jury was told the boiler, a Powermax 155, had received two service visits and about 10 call-out visits, including the day before she was found dead.
Speaking outside the court, Mike Harrison, a principal inspector for the HSE, said Ms Pinkney's boiler was not common but her particular model had been installed into new builds in the late 1990s.
He said British Gas engineers had been called out repeatedly in July 2004 and January 2005.
On 16 March last year Ms Pinkney was found dead in her bedroom.
Mr Harrison said Ms Pinkney's boiler displayed a number of faults and that the gas valve had been adjusted, preventing it from locking out.
This meant that along with not working properly the boiler was also leaking.
The service engineers were given "general training" rather than for the boiler itself, he said.
Mr Harrison said the HSE was still considering prosecuting British Gas over Ms Pinkney's death.
A British Gas spokeswoman expressed her deepest sympathies to Ms Pinkney's friends and family.
She said: "It is obviously something we are deeply saddened by that, for a company that campaigns about the dangers of carbon monoxide poisoning, something like this has happened in one of our own customer's homes."
Speaking after the inquest, Coroner Richard Whittington told the hearing he would be writing to British Gas's managing director, Chris Weston, to outline "my sincerest and grave concerns" with the way customer safety was handled.
A file of evidence seeking a manslaughter charge against British Gas had been passed to the Crown Prosecution Service by the police, but a decision had been made not to prosecute due to lack of evidence.