The engine has a thermodynamic expander (21) for extracting work from a vaporised working fluid (22) that is fed to a feed for it. There is also a condenser (26) downstream of the expander for condensing expanded vaporised working fluid that is exhausting from the expander. A liquid tank (28) is downstream from the condenser, and pump means (29) is located downstream from the liquid tank for pumping out condensed working fluid (38). Further, there is a means for heating (50) and at least partially vaporising working fluid pumped to it from the pump and feeding the heated working fluid to the expander. The heating means itself has at least one inlet for the working fluid pumped to it, and at least one output from which the working fluid is fed to the expander.