Businessman Robert Schenker (31) was found dead in his home in Meynell Walk, Netherton, Peterborough, after being overcome by the lethal gas leaking from his central heating boiler.

A CITY man died from carbon monoxide poisoning after a builder's sloppy repair work on his house left the chimney blocked with debris, a court heard.

Norwich Crown Court heard yesterday the dangerous fumes should have passed harmlessly up a flue pipe, into the chimney and out into the open air.

But the prosecution alleged a botched rebuilding job on the chimney stack in the three days before Mr Schenker's body was found had sealed off the chimney, leaving the gas with no safe escape route.

The court was told self-employed roofer David Johnson (56), of Delph Street, Whittlesey, was to blame after allowing old debris and fresh mortar to fall to the bottom of the chimney while he dismantled and rebuilt the stack.

He denies one count of manslaughter and one of breaching the Health and Safety at Work Act 1974.

The court heard Mr Schenker lived alone in the three-bedroom detached house, which belonged to his father. His parents had another home in Austria and moved between the two properties.

Mr Schenker's family ran a screw-manufacturing business on the Carr Road Industrial Estate in Fengate, Peterborough, and he had studied engineering at Sussex University and for a master's degree in automotive engineering at Coventry University. After working for Ford and Jaguar, he had launched his own business selling parts for Porsche cars.

Prosecuting, Deanna Heer said that in February 2006, Mr Schenker contacted Johnson to repair some damp damage on the chimney breast in his front bedroom.

Johnson, who traded as Merlin Building and Roofing Contractors, told him the brickwork of the chimney stack and lead flashing around it had perished, allowing water to penetrate.

The work was started on Thursday, March 16 and continued the following day.

The court heard that on the Friday evening, Mr Schenker switched on the heating after checking with Johnson it was safe to do so.

But he began to feel unwell and told his neighbour he was "rough".

Johnson finished the work on the Saturday, and on that day Mr Schenker had complained to his girlfriend Vicki Courtman of having a headache and having been sick.

She tried to phone him three times that evening, but got no reply.

The next morning she went to the house and eventually an off-duty policeman she knew broke in and discovered Mr Schenker dead in bed.

Miss Heer said the boiler in Mr Schenker's kitchen was 30 years old and seemed to have been serviced only three times since 1985.

It was found to be producing carbon monoxide by health and safety inspectors, who performed tests which showed the gas took seven minutes to reach Mr Schenker's bedroom.

The gas seeped into the house, the inspectors discovered, because debris was jamming the flue pipe running from the boiler at the point it entered the chimney.

Miss Heer claimed the blockage was made up of old mortar dislodged by Johnson when he had dismantled the chimney stack and fresh mortar which he had allowed to drip off the bricks when he rebuilt it, along with twigs and bird droppings.

She said the fresh mortar had dried to form a "hard slab of concrete" that stopped the carbon monoxide travelling harmlessly upwards into the atmosphere.

The court heard it was hard to know how much debris had already been in the chimney when Johnson started work.

But Miss Heer added there were no signs the boiler had been leaking carbon monoxide into the house for a long time, such as soot stains on it.

Miss Heer said: "In other words, there's nothing to suggest that the chimney had been blocked prior to the time that the defendant was working on the chimney".

She also claimed Johnson's workmanship on the chimney stack was so poor, it had to be demolished later.

The trial continues.