Due to a manufacturing fault with an identified batch of the electricity meters, the clock on the E10 meters can move back by an hour following a power cut.
The fault can only occur where the meter clock is programmed to switch between GMT and BST and the power cut happens during GMT.
This error could mean that an estimated 8,000 customers are not benefitting from the cost of off-peak rate for electricity.
A separate issue has also been identified where a number of E10 meters have been installed with the off-peak times set incorrectly for the customer’s supply distribution area, potentially affecting 8,000 meters.
SSE has said it will check all meters which have the potential to have developed a fault and is writing to any customer who may have been affected to arrange to inspect their meter.
If the meter clock is incorrect, SSE will repair or replace the meter and recalculate the customer’s charges to make sure that, to the best of its ability, they are not left out of pocket.
It is not possible to calculate accurately what a customer’s exact usage split between peak and off-peak units would have been if the meter had been working normally, so SSE will recalculate the charges based on the assumption that 70 per cent of the customer’s units were used off-peak.
SSE’s head of customer service, Jacqui Maxwell, said: “SSE wants to make sure that all of its customers are billed correctly for the energy they use, so we’re committing to check each and every meter that could be affected by a manufacturing fault, replacing it if necessary and recalculating the charges for as long as the meter has been in place to ensure that no customer loses out.”