Companies are being warned to check that any gas appliances on their premises are safe, so that employees and the public are not put at risk.
The Health and Safety Executive (HSE) is urging firms to perform regular checks to avoid the threat of deadly carbon monoxide contaminating the air, which highlights the need for public liability insurance.
Warnings come after a Warwick man was ordered to pay £25,630 after a hearing at Rugby magistrates court for carrying out unsafe work on a gas appliance.
Neil Craig, the HSE's principal inspector for Warwickshire, said rogue workmen can put lives at risk.
"Exposure to carbon monoxide can be easily prevented and simple measures can save lives. If your engineer says you need to have work done to make your appliance safe, please follow the advice given as you may not get a second chance," he explained.
Peter Welke, formerly of Edelston Road in Blackpool, was recently charged with contravening gas safety regulations after conducting work while unregistered and sub-contracting to another unregistered fitter, which illustrates the need for plumbers liability insurance.