Jacinda Ardern's foray into DIY has been a flash in the pan after a Wellington plumber complained that Labour's deputy leader installed her own new toilet.

Justin Will complained to the Plumbers, Gasfitters and Drainlayers Board in February after reading a media report that Ardern replaced her own toilet at the home she shares with television personality Clarke Gayford in Point Chevalier.

The board investigated and chief executive Martin Sawyers this week told Will that Ardern had apologised for her error and the case was closed.

In some parts of Auckland, including where Ardern lives, it is illegal to install a toilet unless the work is carried out by an authorised plumber.

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"Ms Ardern accepted the work she carried out was sanitary plumbing work under the [Plumbers, Gasfitters and Drainlayers] Act and that it was unlawful for her to replace the toilet pan herself," Sawyers wrote in a letter to Will.

"Due to the work being minor and of low risk, Ms Ardern's cooperation, acknowledgement and apology, the board will not be charging Ms Ardern with an offence under the Act but instead have issued her with a warning."

Ardern told the Herald she did not realise when she bought and installed with Gayford the new toilet, to replace a broken down existing one, that they were breaking the law.

"Interestingly enough you can replace your own toilet in Wellington, but you can't replace your own toilet in parts of Auckland and I fall outside the area that you're allowed to replace your own toilet, I'm told, by about a kilometre."

The new toilet was part of a renovation the couple were undertaking late last year and Ardern mentioned it as her proudest moment, prompting the complaint on February 11.

"It wasn't vindictive. I literally didn't know."

Ardern, who was promoted to Labour's deputy leader last week, said she was happy to be investigated by the board and did not expect to be treated any differently from anybody else.

"I don't think I'm above the law."

She did not know the complainant.