Rheem/GE power vent water heater, pilot lites, but not the main

I have a Rheem/GE power vent waterhtr 40 gallon. Been working fine until now. The t'stat calls for hot water and sends a signial to the controler to start the blower and pre-purge the chamber and then to stay on. Then the ignitor starts to send 25KVDC to the pilot and the pilot does light, but the main burner never comes on. The LED flashes the code that its calling for hot water and everything seems to be working fine, just the main burner won't come on. I don't smell LP gas at the pilot opening nor outside near the power vent. Call the service tech and they said to pull the main burner line off the gas valve and check for blockage, if not blocked, turn the gas back on and let the system start and check for gas flow from the main gas valve. Of course being very careful and to shut it off once the odor of LP gas is present. I have no other trouble codes coming up. I believe it's the main gas valve since the unit will run for hours due to the pilot being iginited and the control thinks that everything is fine and is just waiting for the water to get hot for the t'stat to open and shut of the system. Anyone else have a problem like this? Thanks, Dan