Hi marlowjen,
Next time (either if you act as the landlady or the tenant) you should include in the rental contract a clause to specify what would be the notice that you should give (as tenant), in order to do what you want to do, that is, to finish the contract before the date agreed in such contract. You know, this time the problem is the boiler, but in the future it could be that you want (or have) to leave because you change your job, or you have health problems, or you don't like the community/neighbourhood... you know, there can be a thousand reasons.
The best is to reach an agreement with the landlady; you can tell her you want to leave the house because it is (according to your criteria) in no good condition to live, and you are going to leave it the 31st march (for instance). This way she will have time enough to look for other tenants (more than one month and a half).
I say "according to your criteria" because, if you are sure you can demonstrate that there is a real problem with the boiler, then you are in your right to claim for it to be repaired (that's the law, art 21 of the Law of Urban Lettings), but if she ignores you, then you should look for a solicitor to sue her and start a long (and expensive) process.
If you don't think she is going to cooperate at all (if she doesn't accept to finish the rent before the original date), whatever communication I was to send, I would do it through burofax, to have proof of everything. You can ask for this to be done by a solicitor in your area, so you don't lose time and make any mistake.
Hope it helps
This message was last edited by franvidal on 02/02/2012.