I'm a student and currently share a flat with two other girls and last week (22/04/200

our hot water stopped working. We phoned the Landlord on Wednesday morning and told him about our problem he asked us if 'we could just wait until friday and have cold showers' but we said this wasn't right and told him to come and check the problem out. He came round that evening making excuses and saying he couldn't see anything wrong but he would come back the following night. He came round on Thursday and did some more fiddling but our hot water was still not working when i left the flat on Friday night. My flatmate phoned me yesterday to tell me he had been around again but still the problem has not been fixed, he'd hummed and ahhed but when asked if we could phone a plumber he said no. apparently the hot water is STILL not working today.
Is there a legal period by which the water must be fixed?! It will be a week soon and i'm pretty sure this is not legal.