Pilot lights up fine. Once the burner lights it only stays on for a split second before going out; often the pilot goes out as well and has to re-light itself. Once in a while the burners light up and stay on like normal. What could cause this? Our service guy came over today and thought it was the valve. I'm not convinced. Thoughts?

Our service guy came over today and thought it was the valve. I'm not convinced. Thoughts?
Not a heating tech but I tend to agree with you. Your heating guy should know not think.
I would clean flame sensor. If that didn't correct the problem I would replace the flame sensor.