Under the Sale of Goods Act which applied prior to October 2015 goods (house and turf) have to be of satisfactory quality and fit for purpose. This is clearly not satisfactory quality but the applicable period is only a 12 month period and in your case it appears that the was a longer warranty in respect of the grass provided presumably by the supplier of the grass for 2 years.
However neither the statutory 12 month period or the retailer 2 period apply in respect of replacements. It is the overall period which is relevant.
However goods (the lawn) have to be free from manufacturing defects (which would include the subsoil below the turf and the turf itself) for a period of 6 years. After 2 ½ years it would be for you to prove that the defect in the ground or the grass existed at the time of manufacture (when it was all put together and laid). That would come down to whatever evidence you are able to get from the new supplier as to why the old grass died and the new grass has not. Before you rush off to court to claim the cost every turfing, you need to make sure that your new grass is going to last as long as grass normally lasts.
More importantly, you are going to need some written evidence from turf suppliers (the more the better) which says exactly why all the previous grass has died and what work is necessary and has been necessary to put it right.
It would be small claim court claim.
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