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.
A spokesman said: "The issue will be investigated as a matter of urgency and no customer will be charged the extra amounts resulting from errors with the smart meters.
"We would like to apologise to any customers if this has caused distress."
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.