jaybee
Ultimate Member
As I said earlier, there was an upgrade in the material (silicon nitride, less porous and doesn't oxidize like the older silicon carbide) a few years ago, and they are much more reliable than in the past. For the minimal cost, I would still keep a spare.
As for looking at them and telling they are bad ... I can
so can I, if they are discolored, cracked or a piece missing but some have a hairline crack that only flex or raise ohms to trigger a fault at temparature so they look normal at ambient but change at temp in the burner flame.