The company introduced Blue +Price Promise, its first 100% nuclear-backed tariff, in April, with the 'Feel Better Energy' television campaign, featuring a dancing brand character called 'Zingy'.
At the time, it offered customers the chance to fix their energy prices until September 2013.
EDF is in the process of withdrawing the second Blue +Price Promise it launched on 3 August, due to what it said was a surge in demand. The deal replaced the September 2013 offer with the chance to fix their energy prices for the next two winters, until April 2014.
An EDF spokesman said: "Since the launch of the Blue range in April, hundreds of thousands of customers have signed up to our two Blue +Price Promise deals, which offered customers low dual fuel prices, and a guarantee that these energy prices would remain frozen for the entire duration of the tariff."
Last week, EDF told Marketing that more than 500,000 accounts had signed up to the tariff so far.
The EDF spokesman said "a surge in demand in recent weeks for the tariff means our cap on the number of customers we could support based on the energy we have purchased is now close to being reached".
It plans to launch another Blue +Price Promise fixed-price tariff to replace the April 2014 deal.
EDF explained that it buys energy for fixed priced tariffs in advance based on the length of the guarantee and the number of customers it estimates will sign up to it.
Zingy's appearances in TV ads created by Abbott Mead Vickers BBDO have proved massively successful, with the company being deluged with requests to bring out a Zingy toy, according to marketing director Martin Stead.
EDF also carried out what it believes is the largest door drop in energy company history, with a drop to 19.5 million households this year, which featured Zingy.