His home at Allendale Crescent, Penshaw, was leased from gentoo, and the heater had been checked a month before his death, the inquest at Sunderland Magistrates' Court heard.

The throat plate of the living room fire had become blocked by ash and debris.

Mr Terence Knox, a gas service engineer for gentoo, had visited Mr Rutherford's home to carry out a routine safety check on May 24, weeks before he died.

Mr Knox said that although he visited between 40 and 50 properties each week, he remembered checking Mr Rutherford's home.

He said: "I remember the visit because he had an electric organ in the back room and I asked if he still played it. There was nothing out of the ordinary. It was a nice warm day and I commented because he had the fire on.

"I went around with the gas analyser and everything was sound. I threw smoke pellets in the fire and checked outside to make sure the smoke was coming out.

"Then I checked the loft, bedrooms and smoke alarms, then I asked him to sign the sheet."

After Mr Rutherford's death, gentoo housing issued warning statements to tenants about maintaining solid fuel heaters and have now introduced a twice-yearly chimney sweep check.

At the time of Mr Rutherford's death it was policy for their gas service engineers to remind tenants to clean their throat plates once a month as standard.

Mr Knox could not check the state of Mr Rutherford's throat plate because the fire was on, but said that by throwing smoke pellets on the fire he knew the ventilation system was working normally.

Tests showed that Mr Rutherford's blood contained a 47 per cent saturation of carboxyhemoglobin, a sign of carbon monoxide poisoning.
A 50 or 60 per cent saturation is usually fatal, but Mr Rutherford's heart problems meant that he was killed by a lower level.

Coroner Derek Winter said: "I'm given some degree of comfort by the steps that have been taken since this tragedy, but I'm sure there are further lessons that can be learned.

"I'm driven to the conclusion that this lends itself to the verdict of an accident.

"It may have been preventable. I don't know.

"Had gentoo not taken the steps they have taken to improve their systems I would be minded to have written to them to take steps to prevent similar fatalities."

Forensic scientist Mr Mark Tyler said: "Mr Rutherford had inhaled a substantial amount of carbon monoxide gas prior to his death – high enough to be considered life threatening."

Pathologist Dr Peter Cooper supported Mr Tyler's findings.

He said: "I have no doubt that carbon monoxide poisoning is the main cause of death."

Coroner Derek Winter asked Mr Knox why he thought the throat plate had become blocked so quickly.

Mr Knox replied: "After that visit there was heavy downfall. It rained for days on end. That's the only thing I can think of."

Steve Terrance, head of Health and Safety for gentoo, went to Mr Rutherford's house the day after he died with two specialist inspectors.

He said: "One of the inspectors commented on the dust in the house and said he thought it was a blocked throat plate.

"He lit a match in the bed of the fire and the smoke came straight back into the room."

Mr Rutherford's family asked Steve Terrance at the inquest whether gentoo had considered fitting carbon monoxide detectors as standard, but he replied that they felt it would lull tenants into a false sense of security.

MP Fraser Kemp has campaigned for years to raise awareness about carbon monoxide poisoning.

Speaking after the inquest, Mr Kemp said: "First of all I would like to extend my sympathy to the family and friends of John Rutherford.

"Carbon monoxide poisoning is a silent killer that has killed many people in Wearside over the years.

"This tragic death again highlights the need for greater awareness.
"It is important that the campaign to highlight these dangers continues and everyone is made aware of them."

Carbon Monoxide (CO) Awareness Week begins this Monday.

Verdict: Accident.