Hi,
I think it is impossible too. Here it's what I've done:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg713.imageshack.us%2Fimg713%2F8025%2Fpumpsp.jpg&hash=3c80ea6ace70feca96fd29f2e06414749878ebf8) (http://imageshack.us/photo/my-images/713/pumpsp.jpg/)
We know that Wpump < Wsteam because some work will be lost as heat.
So, Qpump = Wpump = Wsteam + Qhome which is impossible.
I've admitted that all the work given to the heat pump will be used to heat the water.