La Cornue publishes two BTU ratings for every gas part on its range line — one for natural gas, one for propane — because the two fuels burn at different rates and need a differently sized orifice to deliver the correct flame at each burner. The twin brass burners are rated up to 17,000 BTU on natural gas and up to 12,500 BTU on propane at the front position, for example, with the rear burner and the French top, power burner and lava-rock grill each carrying their own pair of figures. A conversion means matching every one of those orifices to the gas type actually being supplied, not adjusting a valve or a knob.
Why This Comes Up
The two situations that most often call for a conversion are moving a range between a natural-gas property and a propane one, and installing a range in a home that is being connected to a different supply than it originally shipped for. Either way, the range itself does not know which fuel is coming into it; only the orifices at each burner determine how it burns that fuel.
What Happens If It Is Wrong
A range running on the wrong orifice size for its fuel does not usually fail outright — it burns badly. A yellow, lazy or lifting flame, poor simmer control, and sooting on the burner or the pan above it are the classic signs, and they read almost exactly like a worn or dirty burner. That resemblance is what causes a wrongly converted range to be serviced repeatedly for “a worn burner” without the underlying mismatch ever being corrected, since replacing a burner does nothing if the orifice feeding it is still the wrong size.
Why a Technician, Not the Owner
Refitting an orifice means working directly on a live gas fitting at every burner, the French top, the power burner and the grill where one is fitted, then confirming supply pressure at the range afterward with the correct instruments. It is not a job to attempt with the range connected, and it is not something to guess at from a parts diagram. This is one of the few areas where La Cornue’s own guidance and general gas-appliance practice agree completely: gas connection and conversion work belongs to a technician, full stop.
What to Check Before Booking
If a range has recently moved between properties, or a property’s gas supply has recently changed, and burners are behaving oddly across more than one position on the hob rather than just one, a conversion mismatch is worth raising when you book, since it changes what the technician checks first.
A La Cornue range repair visit will confirm supply pressure and orifice sizing before concluding that a burner itself has failed, and any conversion work is carried out by the technician, not the homeowner.