Hi James Eddie
HMRC will accept probate values for inheritance tax and capital gains tax purposes.
The completion of CG34 (Post-transaction valuation checks for capital gains) is not compulsory, however, if you would like HMRC to check your valuations, you can download the form at
Post transaction valuation checks for Capital Gains (CG34)
The replacement of a boiler, re-wiring of the property, replacing windows, doors, kitchens and bathrooms etc, fall under 'repairs and maintenance' and cannot be set against the capital gains liability.
Capital expenditure, such as when you 'add something to the property that was not there before', 'alter, improve or upgrade something that was existing' or 'include the purchase of furnishings and equipment for the property'. Some examples are 'adding an extension' 'installing a security system if there was not one before' or 'replacing a kitchen with one of a higher specification'.
Please take a look at Work out your rental income when you let property