Melvin Scholes, who traded as Fieldhead Plumbing, was prosecuted by the Health and Safety Executive (HSE) after he carried out gas work while falsely claiming to be registered.
In January 2007 the HSE received a complaint about Mr Scholes from one of his customers and in May that year it became aware of other work undertaken by him in Rotherham.
He pleaded guilty to breaching the Gas Safety (Installation and Use) Regulations 1998 at a hearing at Rotherham Magistrates Court in October.
HSE Inspector Steven Kay said after the hearing: 'It is important for gas installers to keep their competence assessments up to date and to register.
“Re-assessment is necessary to ensure installers have the necessary skills and by being registered they also keep up to date with current issues and practice.
“Illegal installers undercut the reputable ones and adherence to the Regulations ensures a level playing field and a degree of quality assurance for householders.
'Those who try to cheat the system also cheat their customers. Gas safety regulation is there for a reason - to stop people being killed or poisoned by carbon monoxide due to unsafe work and unsafe appliances. HSE will not hesitate to prosecute individuals who carry out gas fitting work while unregistered.'
Workers undertaking gas installation and maintenance work must be registered.
Since 1998 gas installers need to also sit an Accredited Certification Scheme (ACS) test every five years to be deemed competent and maintain their registration. Mr Scholes had previously been registered, but had allowed his registration to lapse.