HELP! Advice from a solictors or law student on housing

I need help with ending a tenancy agreement beffort the tenancy ends.

I moved into flat about 2 months ago but it has had some problems most significantly the heating is not working and the landlord is adamant that I am making it up. I know I can contact my local council to help with this but its gotten to the point that I can no longer live at the flat. I have been trying to seek advice on how to end the contracat but those giving legal aid say my issue is not covered and I have been unable to find a solicitor that will deal with my issue plus I am pretty sure it will be expensive and I don't have money to spend now.

I know I have to 'surrender' the tenancy agreement. I am planning to write to the landlord informing him that informing I will be leaving(which he has informally agreed to). I want to make sure that I write the right thing so I am not liable for the remaining months of rent to pay. Could someone please let me know what to write. Also do I need him to sign it or we both do.

I am in desperate need of help so if you can help it will be very helpful.