My $.02 Woke the other morning to my wife's complaint of, "There is no water!" Never got out of bed so fast in my life! I was pretty sure there WAS water, SOMEWHERE! :) The plastic drain valve was about 4 feet away from the heater and water was running right through the heater. Luckily the heater is in the basement, and there is a floor drain nearby. Caused annoyance, but no damage. Thank you, Mr. Shopvac! Anyway, I tested the T&P relief valve regularly, and it tested fine, so I guess after a certain point you just takes yer chances!
ps the old one was a 'Sears' (don't know who made it) and the new one is a 50 gal. gas GE (by Rheem) for $349 at Home Depot.