death spiral of a water heater
I also do not doubt that when gas heaters enter that death spiral their efficiency drops. But the death spiral will likely differ from normal aging where the efficiency hit will be modest (like I said, I've so far not been able to measure it from background on water heaters I've used.) Having to crank the thermostat up is a warning to the owner that the heater is having trouble. Leaks of course are the other obvious indication that time is up.
[SIZE=3]in our town I get 3 to 5 calls a week wanting me to come out and flush the tank for them.... I tell them that it will be $150 to fool with their 9 year old gas heater that is rumbling all the time and I also tell them that my work is guaranteed for only 30 days... [/SIZE]
Then it begins to build up all over again..
they also want me to try the vinegar suoltions in the tank to clean it and I tell them that it can do more harm than good to strip the lime out of a 9 year old rumbling heater.exposeing any old metal cracks to the water can usually accellerate a leak..
.. and when I tell them its worth about $275 to do this they usually opt for a new heater...
when you hear the banging and rumbling, the heater is trying its best to let you know its getting over the hill...