A WEE COUNTY plumber was found guilty of botching a boiler installation which led to the complete destruction of an elderly couple's home.

Robin and Marion Cunningham were left trapped beneath the rubble when their property was blown to pieces by a massive early-morning explosion.

Workman Craig Hall left a gas pipe liable to come loose in the Callander house by failing to solder a vital 90-degree joint where it attached to the new equipment.

For eight months the fitting was held together by just a little paste used to prepare the joint for connection.

But eventually it separated, pouring gas at up to nine cubic metres an hour into the couple's utility room.

Then, at around 5.45am on March 28, 2013, the gas ignited, "totally demolishing" the property and sparking the evacuation of nine nearby homes.

The stricken couple were later pulled from the wreckage by firefighters. Mr Cunningham, then 77, was taken by air ambulance to Glasgow Royal Infirmary with burns to his head, face, and both hands, and spent a full week in hospital.

Mrs Cunningham, then 74, had less serious injuries, but Stirling Sheriff Court was told she has been left "frail and very anxious" by what happened, while Mr Cunningham's Parkinson's Disease had "obviously progressed".

Their daughter Lynn, 56, said that from leading quiet, independent lives, the couple had been made "dependent overnight" by the blast.

She added that her parents, now aged 79 and 81, had been "utterly overwhelmed" and said: "They actually didn't have the ability to put their lives back together again – it was too much."

After a five day-trial, Sheriff William Gilchrist took less than 40 minutes to find Hall, of Tullibody, guilty of installing the combination boiler "otherwise than in accordance with appropriate standards and in such a way as to prevent danger" by failing to ensure that the gas supply pipe was properly joined to the gas inlet pipe of the boiler.

He told the court: "I'm satisfied beyond reasonable doubt that the failure to ensure that the gas supply pipe was adequately joined to the gas inlet pipe had the consequence of allowing gas to escape, thereby causing the explosion."

Hall, 35, in evidence, insisted that he had applied heat with his blow-lamp to solder the so-called "Yorkshire fitting" between the inlet pipe and the boiler, but accepted that the solder had not "run" and the joint had not been properly made.

Sheriff Gilchrist said heat could only have been applied "very fleetingly", because not only had the solder in the joint not run, but even some of the flux paste applied as part of the process had not melted.

The court heard that it was this sticky paste that held the joint together and allowed it to pass a "gas tightness" test that Hall carried out before firing up the system.

Sheriff Gilchrist – who deferred sentence on Hall until February 7 for background reports – said that soldering the joint but doing it "completely inadequately" could be more culpable than missing the joint among the many joints that had to be soldered, and not soldering it at all.

He said he was not considering a prison term, but Hall could face a fine or a community-based sentence.

The engineer, promoted two years ago to plumbing manager at Stirling-based TRS Plumbing and Heating Services, the company he was working for when he botched the job, looked shocked when the verdict was announced.

His advocate, Susan Duff, said she would reserve her speech in mitigation for the sentencing hearing.

During the trial, Hall insisted that he had double-checked that his work was "gas tight", using two different kinds of pressure gauge, but restricted space behind the fitting-plate of the boiler made it difficult to visually inspect the fitting to check that the solder had run – as required by the relevant British Standard.

He said: "It was just another day's work, another job done."

He added that he had returned to the Cunningham's home in February 2013 – just weeks before the explosion – to adjust a condensate pipe on the boiler, and again smelled no gas.

Hall, a plumber since soon after leaving school, claimed: "You've got a kind of nose for it, having been in the game for many years."

When cross-examined by prosecutor Shona McJannett, he agreed that the British Standards Institution technical standard advice for soldering a Yorkshire fitting stated "the finished joint shall be visibly examined to confirm that solder has run".

He said he accepted that on all the other pipes he had attached to the new boiler, a "ring" of solder was visible.

But referring to the gas pipe joint, he said: "It's in a tight space, you've got a boiler in front of you, a jig plate in front of you, and that's why testing methods are in place as well."

Mrs McJannett challenged: "I don't think you soldered that joint at all, did you, Mr Hall?"

Hall replied: "There was heat applied to every joint."

The court had earlier heard scientific evidence that not only had the solder not run on one aspect of the fitting, but neither had the flux paste, which is used to assist the process.

Sheriff Gilchrist then asked Hall: "How do you account for the fact that the solder and the flux didn't run? If heat had been applied it cannot have been very much or for long if it didn't even melt all the flux."

Hall replied: "At the time I thought everything was fine."

Later in the trial, Ms McJannett described the blast as "a whoosh" that had blown out the complete outer walls of the timber-frame property, in Murdiston Avenue, causing its roof to collapse into the void.