Gary Day, a retired engineer from Abergavenny, has saved himself and three neighbours more than £2,300 after discovering their meter clocks were wrong by several hours. Tariffs such as Economy 7 and Economy 10 offer customers a lower rate for electricity during some hours.
Nearly four million households across the UK are reliant on tariffs, according to the consumer watchdog Which? Mr. Day told Which? "I have only checked four meters and every single one of them was wrong. I am horrified that there might be others that have these clock errors and don't realise it."
Mr Day and his neighbours were all on time-of-use tariffs with Swalec. A spokesperson from the company offered to recalculate any charges for customers whose meter clock is incorrect.
"We will always make sure our customers are not left out of pocket. If anyone suspects their meter clock may be incorrect, or would like us to check, please give us a call on 0800 975 8317."
More top news
At a ceremony in Downing Street today 4 British soldiers - including a nurse from Llandrindod Wells - will receive medals for their bravery
A report commissioned by the Alzheimer's Society estimates that in 2013, the total cost of dementia in Wales was £1.4 billion.
London was in a celebratory mood on 7 July 2005, but everything changed when three suicide bombers attacked the capital's transport network.