Sources:
http://home.howstuffworks.com/home-improvement/heating-and-cooling/how-to-troubleshoot-a-hot-water-and-st
eam-distribution-system.htm, http://www.dummies.com/how-to/content/how-to-maintain-hot-water-heating-systems.html, http://www.ehow.com/about_5312987_forced-water-heating-system-theory.html,
http://www.nytimes.com/1996/02/04/nyregion/home-repair-how-to-keep-your-hot-water-heating-system-up-and-r
unning.html