Christopher Amphlett, 65, and his son Mark, 37, trading as Worcester Windows put a Worcester pensioner at risk when they built a conservatory at her home.
The failed to manage the existing flue of the gas boiler before they started work as they should have done, and then after they had completed the work, they illegally inserted a plastic pipe into the original flue and extended it through the conservatory roof of the ground floor maisonette.
This only came to light when British Gas visited the property three months later to do the annual check. They detected a gas leak from the flue in the conservatory and immediately condemned the boiler.
The Health and Safety Executive found the two men were aware that the flue they put in was defective but had made no attempt to rectify it. Neither of them were registered with the Gas Safe Register.
Both pleaded guilty and were ordered to carry out 150 hours of unpaid community work over 12 months, and pay £2,400 costs.