What are my rights in a six month letting contract?

I have rented a flat privately, and i have been there 4 months and still have not received the gas certificate, I have brought a carbon monoxide detector and it has gone off twice. I do not wish to stay in the flat any longer, is it my right to leave now and not be breaking the contract??? do i have to give my landlord any notice?? i have had enough of waiting now. please only serious answers.