When I light the pilot light it stays lit until I turn the temp up. Then the burner lights and in just a few seconds all goes off. I do it all over again and again with the same results. What next?? Model pr650nbrt 50 gal

when I light the pilot light it stays lit until i turn the temp up. then the burner lights and in just a few seconds all goes off. i do it all over again and again with the same results. what next????? model pr650nbrt 50 gal
To ellettsvillein
You've got a safety taking you out. Is the purge fan running? If not the gas valve will close.
You said your pilot stays lit, so that eliminates the thermocouple being bad, unless you have a continuous igniter.