Peter Naylor, of Wednesfield, removed the gas meter at the property in Arnhem Road to reach a leaking water stopcock he was repairing in December last year.
Wolverhampton Crown Court heard that about 15 minutes after he had left the bungalow to buy a replacement stopcock fitting, the gas exploded, causing a fire which spread through the building. The fire was so bad that what was left of the house had to be demolished.
The Health and Safety Executive (HSE), prosecuting, told the court that householder John Davies, 66, had to rescue his nine-year-old granddaughter from a back bedroom. She was unhurt in the incident, but badly shaken.
However, Mr Davies suffered 21% burns to his face, neck and hands in the blaze. He spent six nights in hospital and required a skin graft to his left arm and hand.
HSE's investigation found that Mr Naylor was not registered with the Gas Safe Register to work on gas appliances and had not isolated the gas system correctly.
Peter Willliam Naylor, of Frost Street, pleaded guilty to breaching Regulation 3(3) of the Gas Safety (Installation and Use) Regulations 1998. He was given a 10-month suspended prison sentence and ordered to carry out 150 hours' unpaid work. The court also ordered Mr Naylor to pay £2,000 costs.
After the hearing, HSE inspector Pamela Folsom said: "This case is a warning to unregistered individuals that they should never undertake gas work under any circumstances. Anybody who carries out work on meters, boilers, hobs, ovens, fires or any other gas appliances without being on the Gas Safe Register is breaking the law.
"Mr Naylor believed he had sufficient basic knowledge to work with gas but he was not authorised to do this and did not follow proper safety precautions. His incompetence caused an explosion that could easily have been fatal, and the resulting fire left Mr Davies with serious burns and a home so badly damaged that it had to be demolished."