An elderly retired law lecturer tragically died from carbon monoxide poisoning from a blocked central heating flue hours after his wife was rushed to hospital suffering from the same condition, it was revealed today.

Eighty-year-old Robert Sinclair was found dead in his Glenavy, Co Antrim home last summer when the emergency services broke in after he failed to collect his wife from hospital.

The flue and boiler of his coal pellet burning central heating boiler had been cleaned the morning before by a chimney sweep, but had then become blocked, causing his wife Patricia's violent headaches after dinner that evening, and his death a few hours later, a coroner concluded at an inquest in Belfast.

Coroner Brian Sherrard warned householders the lesson from the tragedy was that everyone should be particularly vigilant over the possibility of blocked flues in the days after cleaning.

Experts from Forensic Science Northern Ireland and the Health and Safety Executive who gave evidence to the inquest concluded that when the central heating boiler was re-lit after cleaning, a build up of caked-on soot fell down causing a blockage as the asbestos flue expanded with the heat.

When they inspected the heating system they found a sold lump of soot weighing over half a kilo lying at the bottom of the flue on top of the boiler.

With the flue blocked deadly fumes escaped into the house, they said.

Delivering his findings, the corner said: "It seems highly likely that this blockage occurred after the cleaning took place.

"It seems to me a very important lesson can be learned from this death that may be of assistance to other people who have chimneys and flues swept."

He said it appeared householders needed to be aware that cleaning itself could dislodge particles they were not aware of in the flues.

"The best we can do following cleaning is to be particularly vigilant for a number of days afterwards with regard to possible unexpected build up of soot."

Mrs Sinclair said that her husband of 48 years had been meticulous about having the boiler and flue swept every summer.

They had been in the bungalow since having it built in 1976 and never had any problems with the boiler. The same sweep had swept the chimney the entire time she said.

On the morning of August 2 last year the sweep made his regular annual call and swept the flue and cleaned the boiler, and her husband re-lit it, she said.

That night while having dinner Mrs Sinclair, who has angina, suffered a bad headache and chest pains and her husband dialled 999 and she was admitted to hospital.

Doctors told him he could return to the hospital the following morning to collect her.

"They did a test the next day at the hospital that showed I had carbon monoxide poisoning," she said.

Mrs Sinclair said her husband's failure to collect her led to the alarm being raised.

"When he did not come by midday the nurses kept ringing him but he did not answer."

A local doctor was contacted and he went to the house, spotted Mr Sinclair slumped in a chair in a living room at the rear of the house. The Fire Service was called to break in and Mr Sinclair was declared dead at the scene.

Maurice King, who described himself as a part-time chimney sweep working nights and weekends, said he he had used a brush, a scraper and a vacuum on the flue.

"I did a smoke test with a burning newspaper and it was drawing smoke up the chimney," he said.

Dr William Burns of the Health & Safety Executive who carried out one of the inspections of the boiler and flue, said he would be having discussions with the Northern Ireland Chimney Sweeps Association about the build up of residue in flues which sweeping did not remove.