No heating in my house.My landlord will not spend money upgrading or repairing the boiler.?

I moved into my private rented property with my three children under 6 years old in January. I rent from a leading estate agent. When we moved into the property we complained that there was no heating upstairs. There is an an old boiler that throws heat out in the front room only. They did send a contractor around and he advised me that he had already informed the landlord that he should replace the boiler. However, the landlord has informed me that he thinks the property gets hot enough when the heating is on and does not want to spend any more money on the property. The house is so cold that my children refuse to sleep upstairs. There is no double glazing which does not help. I am concerned for the coming winter. I was not made aware of the problem before I signed the tenancy agreement. I have been told if I end the tenancy agreement before the agreed date, that they will keep my deposit. Is this right? can a landlord let a property out to a family with no heating upstairs and deduct my deposit if I end the tenancy earlier because it is simply too cold to stay in the property? Also, just to mention the property was a real mess, I had to pay storage to re house my belongings whilst I sought permission to clear rubbish ETC from the property. Also the electrical items plus cooker do not work properly. Does the landlord have to have a yearly inspection of all electrical and gas items in the property. Many thanks for all your replies.