Millions of households could be owed money by their previous energy suppliers, in many cases amounting to several hundreds of pounds.
When customers move house or switch energy company, they're frequently in credit with their previous supplier - but don't always get that cash back.
And, according to price comparison service uSwitch.com, as much as £235 million of consumers' money could still be lying dormant in the closed energy accounts of 2.7 million homes.
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The uSwitch survey revealed that a quarter of bill payers who have switched supplier admit they don't know whether they have credit remaining in previous energy accounts.
"With six in ten people admitting they are rationing their energy use to save money, any unclaimed funds could go a long way to helping pay this winter's bills," points out uSwitch energy expert Tom Lyon.
Those that do take the trouble to claim are often in for a nice surprise. The research revealed that over half of households that have switched supplier have been in credit at the time, with four out of five successfully reclaiming an average of £88 each.
A quarter said they received more than £100, with some receiving as much as £300.
Energy suppliers launched the 'My Energy Credit' campaign six months ago to help return unclaimed balances to customers - but more needs to be done, says uSwitch.
"It's fantastic to see so many households successfully reclaiming what is rightfully theirs, yet almost a quarter could still be missing out on balances left languishing in dormant accounts," says Lyon.
"We urge the industry to continue with its campaign to help reunite as many consumers as possible with money from old accounts. It's particularly encouraging to see that almost two thirds of consumers who claimed money back said they found the process easy."
There's no time limit on making a claim, and customers should check with any previous suppliers to see if they are due a refund. You'll need to be able to prove your identity, with a passport or driving licence, for example, and proof that you've lived at the relevant address, such as an old bill.
And anyone planning to make a switch should make sure they don't leave without getting what they're owed.
"If you're about to switch, make sure to take meter readings and give them to both companies for a final statement," says Lyon. "This will ensure that your old account is closed properly and you receive any refund due."
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