A fuel voucher is a code that lets you add credit to your prepayment gas or electricity meter when you cannot afford to top up. It is free, you do not have to pay it back. What is a fuel voucher? A fuel voucher is a code, sometimes called a PIN, that adds credit to a prepayment gas or electricity meter. It is designed to help when you cannot afford to top up and at risk of being left without heat or power. It is a grant, not a loan, so there is nothing to repay. Fuel vouchers