EDF Energy is raising its prices for dual fuel customers by 6% from August, which will add £70 a year to the average bill.
The French-owned company says wholesale fuel prices have risen 13% since April, when it last raised prices.
Then, it imposed a 2.7% increase in electricity prices, which left dual fuel customers paying 1.4% more.
EDF is the second of the “big six” energy suppliers to raise prices for the second time this year.
E.On started off this new round of price rises in the middle of June when it imposed a 4.8% price rise – an average of £55 a year – for its dual fuel customers.
EDF said that 60% of its customers would not be affected by the latest move, which includes vulnerable customers already protected by certain price caps.
The energy firm said one of the reasons prices had risen was the intense cold snap earlier this year resulting from the arrival of the so-called “Beast from the East” weather front, which cut gas storage stocks.
That, it said, was compounded by rising oil prices on the global markets, which fed into higher UK wholesale prices for both gas and electricity.
The company said that the regulator, Ofgem, had acknowledged that costs faced by all energy suppliers had increased when it set certain price caps in April.
EDF’s energy managing director of customers, Béatrice Bigois, said: “We know that another price rise will not be welcome, and we had hoped that our limited changes announced in April would be enough.”
She added that, despite “our best efforts” to absorb rising costs EDF can no longer sustain this.
The company would be writing to advise customers of the change, she said, and that those who wished to avoid the increase would be encouraged to choose a fixed price tariff.