You have a claim against the Seller in negligence.
It will help if I explain how claims in negligence arise.
There needs to be
1. a duty of care
2. the duty of care needs to be breached
3. as a result of the breach there needs to be loss or injury
4. the loss or injury resulting from the breach must be reasonably foreseeable.
In order for there to be a claim in negligence, all 4 heads have to be satisfied.
Although a party may be able to opt out of negligence claims in respect of damage to property by having a contract or disclaimer, it is not possible to opt out of personal injury or death as a result of negligence.
The relevant statute is the Unfair Contract Terms Act 1977 (UCTA).
However even a disclaimer in respect of negligence claims with regard to damage to property will only be applicable if it passes the UCTA test of “reasonableness”. You would need to Google the Act to get all the details of that but basically a person can’t exclude liability for claims in negligence in respect of damage to property to basically do what they like, and drive a coach and horses through all their obligations.
The value of your claim would be to put you back into the position that you would have been had the negligence not occurred.
The problem of course is that you cannot beat them with a blunt instrument until they pay up and if having put it in writing to them that you want this money you will take them to court.
They are actually in breach of contract and if you can get this elsewhere as a higher price you could potentially take them to court for the extra cost.
It is often the case that a robustly worded letter from a/your solicitor threatening a court application and an application for costs, may resolve the issue without the need to go as far as court.
On your house insurance you may have legal expenses cover that would pay for the legal cost so it’s worthwhile checking. Some do and some don't.