Faulty electricity meter clocks may have resulted in 16,000 SSE customers on an Economy 10 tariff paying too much for their electricity.
SSE blamed a manufacturing issue for the problem and has said it will get in touch with any customers who may have been affected.
Economy 10 users may have paid an extra 74%
A spokesperson for SSE said: “For customers timing their electricity consumption in order to benefit from off-peak rates, this could mean that some of these units would be charged at the normal rate rather than the off-peak rate.”
Economy 10 tariffs are similar to Economy 7 or White Meter plans, and charge people a lower rate for electricity during a set ten hour period each day.
The faulty meters could have seen customers paying up to 74% more for electricity if they timed their use to coincide with cheaper electricity rates.
Customers will be refunded
SSE has also said that any customer which is found to have been overcharged will be reimbursed.
The company will aim to compensate customers by assuming 70% of usage took place at off-peak times. A spokesperson said is calculation is likely to benefit the “vast majority” of users.