One of the Big Six energy companies has apologised to customers after faulty smart meters told them they would be charged up to £33,000 for one day's power.
The following day the meter said the bill would be £27,022 for the day.
The customer wrote: "Prices certainly gone up @YourSSE @SSE if my smart meter is accurate on my gas use over last few days! like it warm but..."
An average annual bill for a medium-sized house in the UK is around £830.
SSE said it was aware of an issue affecting a "small number" of smart meters and that affected customers would not be charged.
A spokesman said: "We're aware of a number of SSE customers currently seeing inaccurate readings on their in-home display as a result of an issue with a routine software upgrade carried out over the weekend.
"Customers should rest assured that their billing is completely unaffected as the technical issue only affects the digital display in their home.
"We will be contacting any affected customers directly with more information and hope to get their in-home displays back to normal as soon as possible."
Smart meters communicate directly with energy companies and allow customers to monitor their energy use in real-time.
The Government hopes the devices will be rolled out to every home in Britain by 2020.