Details of a solar thermal water pump, which operates using a low boiling liquid is briefly described. The values of efficiencies of such a pump reported by the earlier researchers [1,2] are very low -being of the order of about 0.1 percent. In this paper an attempt is made to find out the reasons for such low efficiencies. A few changes to be made in the experimental set up to improve the performance of the pump re discussed. Also suggested are the modifications required in the analysis to reduce the large difference reported by the researchers between the measured and predicted performances.