The defect was potentially dangerous, PGDB chief executive Martin Sawyers said.
"The wall cavity can fill up with gas, which can then be ignited by a spark given off by the working of a light switch or other electrical fittings."
The court ordered Connon to pay $130 in court costs and a $113 solicitor's fee, as well as the fine.
The PGDB said it was becoming more common for tradespeople to do work they weren't licensed to complete.
The worst culprits were said to be renovators, who pass on costly problems to the next buyer.
The board advised buyers to check any restricted work was completed by a licensed tradesperson before they purchased a renovated home.
Homeowners should ask to see a tradesperson's licence before letting them start restricted work, the PGDB said.
It urged homeowners who suspected restricted work was done by someone without a licence to contact the PGDB.
Information about what plumbing, gasfitting and drainlaying work is restricted and what work DIYers can do without a licence is available on the PGDB website.