Hertford Magistrates' Court heard that he had put a Surrey household at risk by botching a job.
Tony MacTaggart (who also trades as TJM Heating and Plumbing) of Pembroke Avenue, Enfield, Middlesex, lied to homeowners about being registered with Gas Safe, the compulsory registration scheme for gas engineers. (The Gas Safe Register replaced the CORGI gas register on 1 April 2009.)
An investigation by prosecutors, the Health & Safety Executive (HSE), found that MacTaggart installed a gas boiler in Cranleigh Close, Cheshunt between October and November 2009.
When the homeowners complained about his work to Gas Safe, its inspector found the boiler in a dangerous condition.
The Gas Safe engineer disconnected the boiler and alerted HSE to Mr MacTaggart's deception. HSE found he had been claiming to be Gas Safe registered, carrying out work and then tricking registered engineers into signing off the installations by asking them to carry out annual gas safety inspections.
MacTaggart admitted breaching Regulation 3(3) of the Gas Safety (Installation & Use) Regulations 1998. He was fined £ £2,500 and was ordered to pay full costs of £902 plus a Victim Surcharge of £15.
HSE Inspector Stephen Manley said: "It is illegal for an unregistered person to carry out work on a gas appliance. When unqualified workers try to bypass the law in this way they are not only putting themselves at risk of prosecution and a large fine, they are also putting their customers' lives at risk.
"Working with gas appliances is difficult, specialised and potentially very dangerous. Only qualified and registered engineers should attempt it. HSE will not hesitate to prosecute those who break the law in this way."