Npower customers whose complaints have taken too long to resolve could be in line to receive free energy or even have their outstanding debts wiped, the regulator has ruled.
Ofgem said that customers whose ombudsman rulings had been left outstanding for more than 28 days would now receive free energy until the company - one of the so-called "Big 6" energy firms - had fully resolved any issues.
Customers affected by this up until today will also have any outstanding debt on their account written off by npower.
Npower will now write to the 1,000 or so affected customers to confirm any actions it will have to take.
Ofgem senior partner Anthony Pygram said: "We welcome the company's commitment to working with us to put things right.
"We are continuing our investigation into npower's customer service issues and expect significant improvements from the company to address these."
In a statement, npower said it "continues to make steps to improve its service, including halving overall complaints and reducing ombudsman complaints by nearly 10% since the beginning of this year, but sometimes a delay in finally resolving a complaint can occur, for which we apologise".