There’s no set time when gas prices go up. However, Ofgem, the energy regulator, does review its price cap twice a year. If they raise the cap, your bills could rise in April or October as a result.
Another time that you’re likely to see gas prices go up is at the end of your fixed term contract. Once this set period comes to an end, your supplier will put you on a default tariff, this is likely to be more expensive than your previous fixed-price deal.
The best way to avoid this is to sign up for another fixed period when your current contract expires. You can either choose to stay with your current supplier or shop around for a better deal.