Plumbers liability insurance holders have been warned not to carry out any gas fittings unless they are fully registered.
The warning comes after Royston Edward Godsell, 70, of Cheltenham, was prosecuted for a second time after continuing to carry out illegal gas work without being registered.
He pleaded guilty to breaches under Regulation 3(3) of the Gas Safety (Installation and Use) Regulations 1998 and was fined £540 with costs of £1,346.90.
Cheltenham Magistrates Court heard how Mr Godsell supplied and fitted a gas fire at a private property in June 2009, after having being warned on several occasions not to carry out such work.
Stephan Axt-Simmonds, Health and Safety Executive (HSE) inspector, said: "Do not be tempted to use unregistered engineers or friends - you could literally be putting your life at risk."
Earlier this month, the HSE warned public liability insurance holders to be aware of illegal gas fitters after the prosecution of a Burnage man for carrying out work at a property in Grimsby.