Raj Kumar Bagga was re-roofing a garage at a property on Ashbury Avenue in Swindon between 21 September and 5 November 2012. He removed the boiler's gas flue and later partially pushed it back, leaving a two-centimetre gap – enough to leave the elderly resident in danger.
The Health & Safety Executive (HSE), which investigated, told Swindon magistrates that the boiler was left functioning until a separate fault occurred. The resident then employed a registered gas engineer who spotted the gap and isolated the boiler.
Mr Bagga was called back to the property and, despite being told by the occupant he needed to get a registered engineer, he pushed the flue back in, having cut a bigger hole.
The HSE said that Mr Bagga was not competent or registered to carry out any gas work and the fault was only discovered by chance.
Raj Kumar Bagga, of Woodside Avenue, Swindon, pleaded guilty to breaching regulations 3(1), 3(3) and 8(2) of the Gas Safety (Installation and Use) Regulations 1988. He was fined £1,000 and ordered to pay costs of £1,113.15.
After the hearing, HSE inspector Ian Whittles said: "Mr Bagga was not qualified to make adjustments to the boiler. A registered engineer would have disconnected the flue, isolated the boiler during the works, refitted it on completion and finally checked the boiler.
"His dangerous work could have easily led to injury or even a fatality. The garage was attached to the house and fumes would have escaped into the living accommodation.
"Anyone working with gas must be registered as trained and competent to do so and be members of the Gas Safe Register by law. That way customers can be sure they are dealing with an engineer who is qualified to do the job.
"Unregistered gas fitters expose people to unacceptable risks that can prove fatal. Any business or sole trader who carries out work on any gas appliance without being registered is breaking the law and HSE will not hesitate to prosecute."