Hmm- equity & trusts. An executor has a fiduciary duty to the beneficiaries (those who benefit) in the will and must not act in breach of this in any way- this includes actions for personal gain and the like. This also applies not only to positive actions- such as if he sold the house at half its market value- but also applies to omissions, that is, not fulfilling the terms of the will. If the will stipulates- as you say- that the house should be sold by the executor-then s/he is bound to do so- but this all depends on the exact wording of the will as it can be interpreted in a variety of ways. In a typical scenario you should be able to obtain a court order to compel the completion of the wills terms, i.e. force the executor to see the house.
You have only provided very limited details for me to give any useful information as the rules differ under many circumstances- the best advice I can give is simply to visit your solicitor.