I have a State water heater that's around 13 years old. About a month ago, the pilot light went out randomly and I was able to relight it with no problems. A couple of days ago, the light went out again but I was not able to ignite it again using the built-in igniter. After some research, it seems like the likely culprit could be the thermocouple. The model number of the heater is GS650UBRT100.
I found the parts catalog and was able to find the original part through Sears PartsDirect (http://www.searspartsdirect.com/part-number/9000056015/0042/153.html). However, if I order it now, it probably won't arrive for another week.
The Home Depot has a generic thermocouple by Honeywell, and I was wondering if I can use that instead: http://www.homedepot.com/p/Honeywell-24-in-Universal-Gas-Thermocouple-CQ100A1013/202216463
The manual refers to my water heater's part as a thermopile, but the parts catalog says it's a thermocouple, so I'm confused as to what it actually is, and if it's interchangeable. Would I be ok with getting the generic thermocouple for my specific water heater? It says it's for 30mV systems, but I can't find the specification for my specific model.
This is the heater's manual: http://www.statewaterheaters.com/lit/im/res-gas/186221-004.pdf And the parts catalog: http://www.statewaterheaters.com/lit/partslist/res-gas/186298-000.pdf
Also, what are the chances the problem is caused by another part, such as the pilot assembly kit or the igniter? Should I start with replacing the thermocouple and go from there?
On an unrelated note, I've attached a picture of my water heater. I noticed that there's a pipe on the very right with the valve closed. What is this pipe, and why is the valve closed? Thank you in advance.