I had an off-the-peg conservatory installed by builders and was given an insurance-backed guarantee. I discovered the builder had gone bust when problems began to appear so I contacted the warranty company. Now they say the design and materials were to blame and point out a clause in the guarantee making the customer responsible for ensuring that technical specifications are adhered to. Is this reasonable?
The terms of the guarantee must be fair. The exact wording will have to be looked at, but it sounds as though you should bring in a surveyor to see if what the insurers are saying is true. If the design and materials were to blame you may have a better claim against the conservatory manufacturer. I suggest you see a solicitor who can write to the insurance company and advise you further after seeing the contract.