Genesis Energy's pre-pay system of buying electricity is back online after software problems on Sunday evening meant customers spent a chilly night without power.
Genesis public affairs manager Richard Gordon says the electronic payment system "in Charge", is working on Monday after IT specialists fixed the problem.
Mr Gordon confirmed several customers had been without power since 5pm on Sunday and were unable to top up their accounts.
He says 10,000 customers use the pre-pay system, but most had enough credit to keep the power on during the malfunction.
Mr Gordon says Genesis has had problems with the pre-pay system in the past and a full review of the latest glitch will begin on Tuesday.