designer problem

Maintenance

I have a 12 yr old groundfloor flat. There seems to be a horrible problem and after investigation it was found that the extracter fan in the bathroom is not working. Unfortunately it cannot be repaired in isolation and the Management co: said it is a design problem and that the builders had got it wrong as its connected to all other bathrooms all the way up, that all fans have to be replaced and that it will cost a great deal. It turned out its only about £300 per flat and that the managing co has to get the go ahead by the directors who are dithering. As its over 10 yrs old there is no way we can hold the developers responsible as the NHBC guarantee has run out. The smell is so bad its almost unlivable and the tenants have two young children (one a baby) whose health can get affected. Its about a month since I told the Management co: and all they say is they are looking into it. As its not an accident its not covered by the insurance (for all insurance is worth). How do I go about making the Management co: do the repairs or replaccement?. I dont want the tenants suing me if the children fall ill and even otherwise i dont want a child to fall ill because of my property. they have been there 6 years. The developers say if it was a construction fault, it would have been high lighted long time ago. Where do I turn to because I cannot repair mine in isolation as the extracters are all commected I am told. Any ideas and help will be welcome.