Carlene Golightly, the body's priority consumers unit head, urged people to contact the watchdog to discover what benefits they could be eligible for.
She added: "As winter weather starts to bite, households face their highest bills of the year. With average energy bills of almost £1000 a year, thousands of low-income consumers will be stretched to the limit.
"Many could be driven to turning their heating off. It's a danger to health for the elderly, for the long-term sick and families with very young children."
Recent research by energywatch found that many vulnerable customers are also paying more for their energy, with those using prepayment meters being annually charged £195 more for their energy than the best deals available.
Click here to run an energy price comparison, and see if you could be paying less for your gas and electricity.