Weber crossovers and Char-Broil/Nexgrill carryover “bridges” light adjacent mains. A 210 crossover on a 310, or a carryover left collapsed, leaves a dark burner even with a good valve.
Procedure
Light the first burner. Watch whether flame jumps the bridge.
Cold. Inspect crossover/carryover seating on each tube.
Clean ports on the bridge and the first inch of each main — ports.
Confirm you installed the correct length crossover for burner count.
Adjustable carryovers: extend until they actually touch both tubes.
Bent crossover: replace with the model-correct part.
Still dark with bridge glowing: that main tube or valve.
FAQ
Is this the igniter?
If the first burner lights from spark and the second never catches, it is usually gas bridging — not the electrode on burner two (unless you are trying to spark #2 alone).