Martin Lewis has urged households to check their energy account balances after a couple secured a £4,000 refund when they discovered they had been overpaying their supplier for years.
Jill and Brian said they were shocked to learn thousands of pounds had built up unused in credit on their energy account over a three-year period.
The advice was highlighted during the final episode of The Martin Lewis Money Show Live, where Mr Lewis encouraged bill payers to review their balances ahead of expected increases to household energy costs.
The warning comes as consultancy Cornwall Insight forecasts energy bills for a typical dual fuel household could rise by £209 annually to £1,850 from July.
Ofgem is due to confirm the new energy price cap on May 27.
Mr Lewis explained May is typically the best time of year for households to assess their account balances because credit levels should usually be at their lowest point.
He said: "The basic pattern is, over those winter months, you use your credit or you build up debt, depending where you are."
"That bottoms out just around May and then you start to build up credit until it peaks in November. If you've got a lot of credit right now, this is the point where you shouldn't have a lot of credit, which is why this is the perfect time to be checking."
Mr Lewis said households should generally avoid having more than six weeks' worth of direct debit payments sitting in credit during May.
He advised customers with larger balances to consider contacting suppliers and requesting part of the money back. Jill and Brian decided to investigate their account after watching an episode of the programme in November 2025.
Jill said: "We were paying around £260 a month, which to me seemed extraordinary."
After contacting their energy provider, the couple discovered they had been consistently overpaying for three years.
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Brian said: "When I phoned the energy provider, they actually went back and checked and we'd been overpaying for three years."
"There was £4,500 in credit. I left £500 in the account so we ended up with a £4,000 refund."
The advice comes as households prepare for another expected rise in energy costs later this summer.
Cornwall Insight's latest forecast predicts the Ofgem price cap will increase to £1,850 from July, representing a rise of 13 per cent from the current annual figure of £1,641 for a typical household.
That would leave households paying an extra £209 a year at a time when many families are already facing rising living costs.
Mr Lewis also provided viewers with a practical example of how his guidance could apply to individual households.
He said: "My rough rule of thumb: if you have more than a month and a half's worth of direct debits in credit right now, I would want it back.
"So if you pay £200 a month, you got £300 in credit, that's fine – but for £500, I'd want £200 back."
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