EXPERTS found carbon monoxide seeping into an elderly woman's lounge from a faulty gas fire, a court heard.
Property owner Christine Lynn Sykes admitted a charge of failing to maintain a gas fire in a safe condition.
She also pleaded guilty at Huddersfield Magistrates' Court to failing to ensure that gas appliances in three houses had been checked in the previous 12 months.
The magistrates fined her £700 and ordered her to pay £3,750 costs, after telling her she had failed in her responsibilities as a landlady.
The court heard that Sykes owned three cottages in Westgate, Almondbury, which were let to tenants when the offences happened last year.
Michael Elliker, prosecuting for the Health and Safety Executive, said gas safety regulations were introduced in 1994 after deaths from carbon monoxide poisoning.
Sykes, who owns the Tunnel End Inn at Marsden, was reported to Kirklees Council by one of her tenants in August, 1999.
The HSE had asked Sykes for copies of check certificates.
Mr Elliker said that certificates were produced dated February, 1999. But if the case had gone to trial, one of the tenants would have given evidence that she was convinced no such checks had taken place.
The tenant had changed the locks before February, 1999 and no-one could have got into the property, said Mr Elliker.
Sykes received another letter asking for certificates the following year - but there was no response.
A representative of British Gas then visited all three cottages.
Mr Elliker said: "The gas fire in the lounge of one cottage was eight years old.
He said it was dangerous, producing carbon monoxide which was finding its way back into the room. A blockage in the flue was found.
The fire had not been serviced for some considerable time, and the engineer immediately condemned it and required it to be disconnected.
"The occupier was a lady in her 80s. It is not the prosecution's case that anyone was harmed, but there was a risk," said Mr Elliker.
He added that they had been fully prepared for a trial, but then Sykes had pleaded guilty.
Sykes, who was unrepresented, said she had engaged a Mr Griffin to check the gas appliances.
"Have I been paying good money, and he has said he has carried out these works and not done so?" she said.
"As far as I know everything was fine. Perhaps I have been too trusting."
After the case, Brian Arnold, of the HSE in Leeds, said: "We hope this will be a warning to landlords.
"The HSE and local authorities take gas safety extremely seriously.
"We investigate a number of deaths each year caused by carbon monoxide poisoning, primarily because appliances have not been serviced regularly."