no heat

I moved into rented accommodation 2 weeks ago, i have a short assured tenancy for 6 months. I paid £550 deposit to my landlord but got the first months rent free to allow for decoration and carpets. Since moving in i have had no heat as there is a problem with the gas central heating i have been chasing my landlord for 2 weeks now regarding this he did send out a plumber, not a registered gas engineer,to fix the problem but it still hasnt been fixed, i contacted my landlord again and he said he would get another plumber to come look at it but that plumber never showed up. I have a 13 year old child in the house and its freezing if this continues where would i stand with ending my tenancy early. I live in Scotland where i know laws can be different.