Centrica, the owner of British Gas, reported a £362m statutory loss.
The combination of the pandemic, warmer weather and lower commodities prices led to the loss.
The group said that it would not pay out a divided. Centrica shares fell over 3% in early trading.
Operating profit at British Gas was 35% lower at £80m.
With the results, Centrica announced plans to be a net zero firm by 2045. This is five years ahead of previous plans.
Chris O’Shea commented: “We have made a good start to the turnaround of Centrica, with the sale of Direct Energy now complete and our significant Group restructure on track.
“However, our journey to transform has only just started, as we seek to restore shareholder value by improving customer experience, retention and employee engagement, while maintaining a strong balance sheet. It won’t be easy, but I am confident we have the people, the brands and the market positions to deliver a successful turnaround in the coming years.”