I have been working on this project for a few weeks and figure its ready to be published.
The short of the story is that I am using an Arduino Yun, an Android application and a Power Switch Tail to control a Grundfos pump for the purpose of priming a hot water loop.
The details are available at the link below.
Please let me know if you have any questions.
Thanks.
Yes, couldn't you post some more details here?
Asking 160538 users to click an external link, does not really generate any value for this forum.
Nice application,
It is a good example how to use the YUN with python (not have the time to play with a YUN yet)
-> bookmarked!
The idea is simple enough, you add a T at the furthest point of the hot water system and a water line back to into the bottom of the hot water heater. From there the laws of thermodynamics take over hot water rises, cold water falls and when I turn on the shower I don't have to wait for hot water. The trade off is that the loop is constantly loosing heat that has to be replaced by the water heater.
Does this really work well? How fast is the water moving (or is only the heat moving?
Can you add isolation to the hot pipe to lessen the heat loss?
Peter_I:
Yes, couldn't you post some more details here?
Peter, the value for this forum can be found in my previously made post(s).
robtillaart:
Does this really work well? How fast is the water moving (or is only the heat moving?
Can you add isolation to the hot pipe to lessen the heat loss?
Sorry, past the basic principal of thermodynamics I don't know much about how it actually works. If its the water flowing or simply heat transfer through the water... 
Thought... as I think about it... it must be water flowing rather than heat transfer. The spring check valve stops the water flow and loop goes cold.
I have insulated as much of the pipe as I could as some is inaccessible, I can only assume that it helps reduce heat loss.