At least, the service place charged me to replace the TC.  I made sure I drew the gas up through the stove.  ??

Did they just replace the thermocoupler and not try it? Surely they had it stay lit there... Have you called them on it? Is it lighting and not staying lit, or not lighting at all?

Only a couple of other things that I can think of... blockage in the LP line, or the circuit board.

The thermocouple is a safety device that stays open and lets the gas flow, depending on the temperature of the flame. If the flame is too low, and the thermocouple is set to close at a cooler temperature, it will shut off the gas valve. Most gas nozzles have an adjustment for the flame pattern, by using a variable air source which is a simple regulation. The flame should be an aggressive bluish colour, with little or no yellow showing. It should be a forced flame under pressure, and not weak and burning at the end of the orifice similar to a burning match.

The orifice is what determines the volume of gas that feeds the flame. Propane contains some oil, which can build up around the orifice and accumulate dirt. The orifice diameter is critical, and any obstruction will cause a weak flame, and shut off the thermocouple. This should be inspected and kept clean.

The start up of the flame is usually hotter than the running flame. A thermocouple will recognize this temperature increase, open and allow the flow of gas. Sometimes the running temperature will be less than the thermocouple setting, and then it will close, shutting off the flame.

Gard

They said they left it on for a long while to test.  I should have stayed the extra 5 minutes to check  it.

It was the regulator.

I'm glad you were able to find the source of the problem. It's interesting that the mechanic that replaced your TC, didn't look at the flame strength or test the system pressure using a manometer. Too many technicians are becoming parts changers, instead of diagnosing the problem.

A low gas pressure from a faulty regulator, certainly would effect the burner flame. I'm surprised your other gas appliances weren't similarly affected. Had they been also affected, it would have been easier to trouble shoot the problem.

BOL  Gard