A Suffolk heating engineer accused of killing a customer by failing to properly service their boiler has attributed the deadly build up of poisonous gas to a sudden malfunction he could not have foreseen.

Peter Sykes, 68, told Norwich Crown Court he had thoroughly cleaned Annette Coe’s oil-fired heating system during an annual service on October 19, 2012 – just 47 days before she was found collapsed at her home in St Edmunds Road, Ipswich.

Mrs Coe, the 72-year-old mother of William Coe who runs Coes stores in Suffolk and Essex, was pronounced dead from carbon monoxide poisoning the following morning, December 6.

Sykes, who denies manslaughter by gross negligence, is accused of not clearing the chimney flue thereby allowing poisonous gas to circulate Mrs Coe’s home at fatal levels.

Giving evidence yesterday, Sykes, of Castle Road, Hadleigh, claimed a sudden fracture in the heat exchanger – where fresh air meets heated air – had caused the failure as it was the only part of the system he had been unable to check. He said it was not practically possible to do so.

However Sykes insisted he had carried out a thorough inspection of the system on October 19 and also claimed it was clean and operational when he returned to the property on December 3 to fit a replacement solenoid coil.

The self-employed heating engineer, who had carried out annual inspections at the house for more than 40 years, gave the court a detailed account of the steps taken during an inspection, the tools he used and the checks made to ensure adequate safety.

He said he followed a methodical routine from which he never deviated and would always check the flue and chimney for blockages.

“That would be the most important thing,” he said. “It’s a case of life and I value life a lot more than just skipping and skiving on a routine.”

Sykes also denies three further health and safety charges relating to Mrs Coe’s heating system and two other customers.

He disputed expert accounts of failures found in the heating system belonging to Melvyn Smith in Raydon.

And he said the high carbon monoxide readings found in Mary Blyton’s gas heating system in Woodbridge could be explained by the 15 month interval since his last inspection.

Although he admitted he should not have been servicing gas systems at all as he was no longer registered to do so, he said he only did it for friends.

Sykes told the court he had not worked since Mrs Coe’s death and said he had received more than 100 letter of support from customers thanking him for his service.

The trial continues.