Gas heater burner

[dvdgspncr]

Am a hvac student working on a older 150 highboy gas furnace Burner goes out within 1 minute before blower comes on. Have changed limit on heater as well as one that has the dial on it, thermocoupler, fan relay,scratched my head , crossed my fingers and still same problem. Gas valve is all thats left that I'm aware of that it can be. Anyone with something else to try? Also I have 24 volts at gas valve before ,during and even once burner goes out.

[heatseeker]

do you have 24 vcoming out of the valve if so have you traced it back all the way back to make sure there is not a short somewhere. It's possible that you have a bad ground or loose wire if the valve is opening then the valve is probably good. There has to be a reason just keep digging.