Energy firm SSE has apologised to customers after malfunctioning smart meters told some of them the would be charged up to £33,000 for a day's power.
The company, one of the "Big Six" energy providers, said it had launched an urgent investigation into the matter.
Dozens of shocked customers began to tweet at the company with images of smart meters quoting thousands of pounds charges for a day's worth of electricity.
The average annual bill for a medium-sized house in the UK is around £830.
One account holder tweeted SSE with a photo that said they had used £33,183 of gas in just 24 houts - nearly three million percent over their budget.
The following day the meter said the bill would be £27,022 for the day.
The customer said: "Prices certainly gone up @YourSSE @SSE if my smart meter is accurate on my gas use over last few days! like it warm but .."
SSE said it was aware of an issue affecting "a small number" of its 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."
The government has backed the roll-out of smart meters, which feedback informaiton on household energy consumption directly to energy suppliers and allow customers to monitor their energy use.
The latest figures show there are 4.9 million meters in homes and businesses across the country.