The firm was due to demonstrate the machine at London's Kinetica Museum on Thursday.
The generator was placed in a Perspex box to prove that there was no power input, and surrounded by webcams so that internet users could view the demonstration.
Sean McCarthy, chief executive at Steorn, said: "Technical problems arose during the installation of the unit in the display case on Wednesday evening.
"These problems were primarily due to excessive heat from the lighting in the main display area.
"Attempts to replace those parts affected by the heat led to further failures and as a result we have had to postpone the public demonstration until a future date.
"We apologise for the inconvenience caused to all the people who had made arrangements to visit the demonstration or were planning on viewing the demonstration online."
The failure will only add weight to arguments that the machine cannot work as advertised.
Steorn took out a full page advertisement in The Economist last year asking scientists to test the invention, and the chosen panel will announce their results by the end of the year.
Steorn claims that power is generated using "time variant magneto-mechanical interactions" that occur naturally and are thought to be nearly infinite in supply.
The law of conservation of energy states that all energy cannot be created but simply transfers into different forms.
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