An Open Market Valuation is NOT a survey. It is only a limited check on the property that your mortgage lender carries out to ensure it’s worth the money they’re lending you and is the minimum requirement for lending purposes.
A professional detailed Valuation is always recommended in addition to what your lender requires, as we can identify potential structural and other issues, allowing you to be better informed to perhaps negotiate on price and reassure you about the wisdom of your future investment.