Hey, just made a simple beta arduino sketch to control my circulation pump for my hot water sun collector, you can grab it if you can use it for some other sketch. Also useful as controller for automatic air sun catchers with temperature controlled fan. (i also work on a arduino sketch for this)
You can get the code here http://techmind.dk/arduino-singleboard/solfanger/ Sorry, language is in danish, but comments in code are in english. You can use google translate on the page.