Empire RH65 B vent- Pilot goes out....Help

Hello,
we have an empire RH65 propane B-vent heater and we replaced the thermocouple to try to correct the pilot problem but it didnt help...heater does the same thing.....

this is what happens....depress the pilot button to get started, but we light the pilot flame with a lighter because the piezo sparker has no wire. (this is a "used" heater which worked last year but gave trouble toward end of season. it had piezo ignitor broken when got it.)

but when you release the pilot button after depressing for well enough time..several minutes, the pilot goes out.Pilot will go out when you turn the knob to ON position to light main burner too. the pilot flame is big and blue and covers the thermocouple. There does not appear to be any "adjustment" on their placement anyway, they have a set bracket.

So...any ideas? is there some "magnet" in the valve body that goes bad, turning gas flow off? or does the crazy vent blocking "eco switch" go bad? if there was dirt in the pilot orifice...would that produce a poor pilot flame? The pilot flame is good size. The propane tank regulator, as far as I know is producing adequate gas pressure to the heater itself.

this seems to be a common problem with b-vents....any help on the specifics of this model would be very helpful. Thank you.

Thank you for the info. the model is an RH65B-6, Propane gas, serial number 0407291571, manufactured in 04/06. The gas valve is a Mertix Maxitrol GV31.

Still having trouble with the heater. Jumped the "spill switch" or "eco switch" wires and also checked them for deterioration at the valve end but they are OK. The pilot light goes out when you release the pilot button. The pilot is a large blue flame and in contact with the new thermocouple. We even tried "pre-heating" the thermocouple with a small torch to speed up the process. When we did this, we were able to get the main burner to light but it only ran for about 5 minutes and then a big "click" and the burner shut off abruptly. Took the plastic cap off the valve body and found a round metal circle with +/- adjustment on it.....do you think this adjusts a solenoid shut off on the valve body? Can the valve body be bad...not necessarily the valve but does it have a magnet shut off inside. I have seen these pictured on parts breakdowns for the 25,000 and 35,000 BTU Empires....but not the 65,000 BTU parts breakdown. Thank you. Val

http://www.mertikmaxitrol.com/pdfs/gv30_60/GV-CC-EN-07.2010.pdf
here is some basic info on the valve, and contact info for the maker....