Your landlord is responsible for repairs if you rent from a housing association or other non-profit landlord.
What you can do
Contact your landlord to order the repair.
Your tenancy agreement with your landlord gives you the right to get repairs done within a reasonable time.
Also see advice about repairs in social housing on the Shelter website.
If the landlord is not responding to your requests
If you are not satisfied with your landlord's response, you can make an official complaint. Your landlord's website will tell you how to do this.
Find your landlord's details at: www.housingnet.co.uk/housingassociations