The gas lava-rock grill, one of the module options on a Château cooktop, works by heating a bed of volcanic rock from below with a gas burner, then cooking food on a grate set over that heated rock. It is a different mechanism from a plain gas burner, and it depends on the rock bed itself staying in usable condition — which is exactly the part that gets skipped when a grill is cleaned the same way a French top or a set of burners is cleaned.
How the Rock Bed Clogs
Grease and food residue drip down onto the lava rock during cooking and, over time, coat the rock’s surface rather than burning off completely. A coated rock bed does not transfer or hold heat the way a clean one does, which shows up as the grill running cooler than it should, heating unevenly across the grate, or taking noticeably longer to reach cooking temperature than it used to — all of which can look like a burner problem when the burner itself is working exactly as designed.
Distinguishing Rock Buildup From a Burner Problem
A burner that lights normally, holds a steady flame, and still produces weak or uneven heat at the grate is describing the rock bed, not the burner. A burner that will not light, sparks without catching, or produces a visibly abnormal flame is describing the burner or its ignition system instead, the same as it would on any other part of the range. Knowing which of those two things is happening changes what gets checked first.
Maintaining the Rock Bed
Lava rock is not cleaned the way enamel or a cast plate is — rather than scrubbing it, the rock is periodically replaced once it has become heavily coated, since grease baked repeatedly into porous rock does not fully clean back out. How often that replacement is worth doing depends on how heavily the grill is used, but a grill that has noticeably lost heat performance over time, despite the burner working correctly, is the clearest sign the rock bed is due.
Before Cleaning Around the Burner
Removing the grate and rock to clean underneath should only be done with the grill off and fully cooled, and if at any point that area smells of gas rather than just cooking residue, stop — leave the controls alone, ventilate the room, and call for help from outside rather than continuing to work around the burner.
When It Is Not the Rock
If the rock bed has been replaced and the grill still heats unevenly or runs cool, the burner underneath — its port condition, its orifice, and its flame — is checked the same way any range burner would be, since a clean rock bed on top of a restricted burner will still perform poorly.
If your lava-rock grill is running cooler or less evenly than it used to, a La Cornue cooktop repair visit checks the rock bed and the burner separately before recommending a fix.