If you want the Housing Association to act you have to do things properly. I strongly recommend you go to the Citizens' Advice Bureau with photos of the problem.
However, if you don't want to do that, do as I suggested in the first instance and keep a copy of the letter. State that you want a 'meaningful reply within 14 days'.
Be prepared for a fight. If you get no reply, crank the pressure up by sending a copy of your letter, and photos, to your councillor, and ask for his (or her) intervention. Stress how worried you are about meeting your fuel bills this coming winter.
You can also take them to court, for failing in their duty as landlords.
But get ready for the fight,and get your letter in the post.
If you have children, or an illness or disability, stress this as it will help your case.