Fact-checkers have written to Liz Truss to urge her to publicly correct statements she has made about the energy price cap.
Speaking to local radio stations on Thursday, the prime minister said a number of times that people would not face bills of "more than" or a "maximum" of £2,500.
Yet the energy price cap limits the price per unit of energy, and the £2,500 limit is the average bill cost. People are charged for how much they use.
Government figures say a typical detached house will pay £3,330, a semi will pay £2,650 and a purpose-built flat £1,750.
Full Fact, a fact-checking charity, said it wrote to Ms Truss on Wednesday to stress "it is vital the public have accurate information about energy bills in the context of the ongoing cost-of-living crisis".
Will Moy, its chief executive, said: "We wrote to the prime minister about getting this wrong only yesterday. The government's energy plans will affect every household in Britain this winter.
"And yet Liz Truss has repeatedly misled listeners this morning.
"She must now publicly correct her mistake to make sure people are not misled about their energy prices and hit with unexpected and unaffordable energy bills this winter."
Although Ms Truss initially described the figure as being for a "typical" bill during an interview with BBC Radio Nottingham, she went on to say: "The biggest part of the package we announced is the support on energy bills, making sure that people across this country are not facing energy bills of more than £2,500 and that businesses can get through this winter."
During the next interview, she stated: "We have taken action by the government stepping in and making sure that nobody is paying fuel bills of more than £2,500."
Vulnerable elderly at risk
She repeated the claim on BBC Radio Leeds, saying: "The action we've taken on energy bills will mean that Leeds and other people in West Yorkshire aren't going to be facing energy bills of £6,000 which is what was forecast, they're going to be, through the energy price guarantee, the maximum will be £2,500."
In a tweet on Thursday, MoneySavingExpert.com founder Martin Lewis wrote: "The reason it is so important not to communicate that there is a £2,500 cap [is] it risks some people, possibly vulnerable elderly people, thinking they can keep the heat on max all winter, and they won't pay more than a certain amount."
Sky News Online has contacted Downing Street for a comment on, or clarification over, the prime minister's interviews.