Thanks for your question.
The landlord is under an obligation to keep the structure and exterior of the property in repair. If the window is in disrepair because it is not adequately insulated then you can ask that it is repaired. If however it is as well fitted and insulated as it possibly could be then you will not be able to insist on repair because the property would have been let to your daughter on this basis and she was aware of it.
If the window is inadequately insulated she should formally write to the landlord (copying in the agent) specifying the disrepair, making a list of the reasonable repair required and ask that he make those repairs within a reasonable time (eg. 14 days). State that if the landlord does not make the repair within that time she will pay to have the repairs made and will seek to claim the expense from him and are prepared to make an application to court if necessary.
If the landlord does not make the repair you can pay to have it done and then write formally to him requesting the payment of the cost, again within a reasonable time). If he does not pay you can issue a claim for the money yourself through Her Majesty Courts Service's online service: http://www.moneyclaim.gov.uk/. Write to them first asking for the money and stating that you will issue a claim if it is not received.
Its pretty cheap and straightforward to use.
Open a file, send letters by registered post, keep copies of everything for use in any claim you may choose to issue at a later date.
Again though it does depend on whether the window is in repair or not, if the low temperature is simply because that's what happens with properly fitted windows of that type then she will probably not be able to insist the landlord makes remedial works.
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