A.O. Smith - Promax, Model# GCV 40 00L010000, Serial# B05J023194. Pilot went out, followed all instructions. Everything seemed to work correctly, but pilot would not remain lit. Auto pilot ignitor worked, while holding down On/Off/Pilot knob, pilot lit, held down for 1 minute, On/Off/Pilot knob popped back up, but pilot would not stay lit. Tried several times.

A.O. Smith - Promax, Model# GCV 40 00L010000, Serial# B05J023194. Pilot went out, followed all instructions. Everything seemed to work correctly, but pilot would not remain lit. Auto pilot ignitor worked, while holding down On/Off/Pilot knob, pilot lit, held down for 1 minute, On/Off/Pilot knob popped back up, but pilot would not stay lit. Tried several times.

The pilot has a flame detector on it that keeps the pilot lit once it sees a flame. Sounds like the flame detector is bad. Could also be the regulator,, that is where the flame detector connects. I would change the pilot assembly

That model has a thermocouple according to what I saw on the company web site; therefore, you need to replace the thermocouple and when you install the new one make sure that only 3/8" of tip is in the flame. No more than that or it will fail.