It may not be completely by the book, but I would suggest the following:
Write one last time to the letting agency outlining the problem and state that if it is not rectified within, say 10 days you will proceed with the repairs yourself and deduct the amount from the next rent payment, forwarding on the receipt.
I agree with Callybags, and I'm a landlord. Repairs have to be prompt, particularly if it's urgent, which this is not, but it's not acceptable having to contact the agency on a weekly basis. Sometimes things can get overlooked in an office, but the second reminder and they should have sorted it out.
It may not be completely by the book, but I would suggest the following:
Write one last time to the letting agency outlining the problem and state that if it is not rectified within, say 10 days you will proceed with the repairs yourself and deduct the amount from the next rent payment, forwarding on the receipt.
It is actually by the book, if the landlord/agent is not fulfilling his obligations.
A letter should have been sent (and a dated copy kept) at the start, stating the problem and giving the landlord "a reasonable time" in which to rectify the matter. A "reasonable time" will vary depending of the importance of the issue to be resolved but usually a maximum of 14 days would be considered reasonable.
In this case, as you have already been in contact with the landlord/agent, and considering it is now winter - I would suggest 5 days is very reasonable.
If your friend has to get someone to do the job, he should try to get 3 quotes and accept the lowest.
Thanks for your help Facetious, Bronte , Ajapale and Callywags, I have passed on your replies and I am sure this is the information he needs , Ajapale sorry for posting on the incorrect sub forum, I realised it myself later on.
I agree with what everyone else has been saying, but would really like to stress the following: "Paper Trail, Paper Trail, Paper Trail".
Make sure you are documenting when the calls are made (if they occurred in the past, estimate to the best of your ability), if you talk with someone record their name etc. And send them things in writing so that you can keep a copy. Send it certified mail even for the final notice saying you will be repairing it and then billing them for it etc.