Dixon was fined $1500.
Gasfitting is a restricted trade because substandard work can have serious adverse effects on public health.
Prosecutor Nife Pelesasa Kalavite said they accepted Dixon might not have been aware it was against the law, as he had been working in Australia when the regulations were changed and was never notified by his supervisor.
There were no defects in the work, which was a mitigating factor, she said.
Defence lawyer Jamie Waugh said there was "no risk at all to the homeowner".
"What he didn't realise was that he was no longer allowed to do what he had been doing his entire life," Mr Waugh said.
He said the offending was on the lowest end of the spectrum.
"I struggle to imagine how anything could be at a lower level."
Mr Waugh said that Dixon was "very experienced" and that he carried out his work with meticulous skill and care.
He told Judge Stephanie Edwards the message needed to be sent out to practitioners that they need to be aware of changing regulations.
Dixon's case was far less serious than any similar cases, he said, comparing it to the Santamaria case in 2012, where a qualified electrician carried out gasfitting work despite having no licence, experience or certification for gasfitting.
Santamaria's work was defective and posed a significant risk to the homeowner, and he was fined $10,500.
Judge Edwards said the seriousness of the charge was indicated by the maximum penalty.
She agreed the offending fell at the "very lowest end of the spectrum".
Mr Waugh said an end point fine should be $750, while the prosecutor argued for $3000.
The company Dixon worked for had already been convicted and fined.
Judge Edwards said there were "good reasons" why Dixon was unaware about rule changes.
She fined him $1500 and ordered payment of a solicitor's fee of $113.