The pilot lights, but the burners never fire up. The pilot stays lit. The blower never comes on but will run if manually set to on.
It is GE Ambassador II gas furnace.

Batteries in the tstat are good and it seems to be working fine. Breakers are on.
The pilot is nice and blue.
There is a sensor rod next to the pilot that the pilot heats.
The sensor goes to a relay that is wired to the gas valve.
The relay is marked White Rogers3049-111, WG 35X170.
I suspect this is the problem but I want to be sure.
I have a clamp meter and could not detect 24v on any of the wires going from the relay to the valve.
But "not" seeing something doesn't seem as certain.

Is there anything else I can do to verify this is the problem?
Are there other components that could cause these symptoms?

I did brush and vacuum the burners.
I also tried lightly cleaning the sensor rod with a wire brush.