An advert for one of Dyson's £400 fans has been labelled misleading by the Advertising Standards Authority (ASA).
The video, for the company's Pure Hot and Cool Fan, suggests the fan is cordless when it actually needs to be plugged in, it said.
Dyson told the ASA it did not think there was "any reasonable prospect" of consumers thinking a tower fan or purifier could be cordless.
But after examining the ad, the ASA ordered it should not be shown again.
No power sockets or electrical leads could be seen in the ad – until the final shot, when a cord appeared which was "very thin and coloured grey on a light background".
"The cord was the same colour, thickness and approximately the same length as the edge of the carpet which appeared opposite it on the screen," the ASA said.
Dyson had argued that its fans had been on the market for more than a decade.
"None of those products had ever been cordless nor been advertised as being so," Dyson told the ASA.
Dyson said if the fan were cordless, it would advertise the fact clearly
"If Dyson were to create a cordless purifier it was reasonable to assume that this would be one of the key features which they would advertise."
The ASA was not convinced.
It told Dyson in future not to imply that their fans were cordless unless they actually were.