La Cornue oven cooks unevenly

The three free checks the manual itself lists

Level: a dish of water on the shelf should sit at one depth all over — if it is deeper at the back, the range needs raising at the back or lowering at the front. Door seal and catch: the door has to be held firmly against the seal, and a strip of paper closed in it should not pull out freely anywhere. Trays: nothing larger than the specified size, and space left between two loaded shelves so heat can circulate. All three are in the guide, all three are free, and between them they explain most of these calls.

What it usually means, by the kind of La Cornue appliance

La Cornue sells one appliance in several forms, and the same behavior points at different things on each of them. A built-in side-by-side and an integrated column are not the same service situation, and a dual-fuel range and an induction range fail in different halves.

• Château vaulted gas oven — Radiant heat from below and around, with an electric broiler above. Unevenness front-to-back is normal; side-to-side is not.
• Château vaulted electric oven — Elements top and bottom. A partly failed element produces a clear, repeatable pattern.
• CornuFé convection ovens — A fan is meant to even this out, so uneven cooking in a convection oven points at the fan first.
• Château Tourelle — Multifunction, so the mode changes which elements run and therefore the pattern of the unevenness.

What a vaulted oven is actually for

The voûte cooks by radiant heat from the mass around the food rather than by moving hot air through it, and the graded heat is a feature — it is why a roast in one develops a crust the way it does, and why a Château gas oven has no window to lose heat through. An owner arriving from a fan oven, where evenness is the design goal, reasonably reads this as a defect. A fair proportion of these visits end with measurements inside specification and a conversation about shelf position and turning a roast, and that is a legitimate outcome of a diagnostic rather than a wasted call.

When the pattern is a part

Failures give repeatable patterns and design gives gradients. An oven that is consistently pale on the left half, or that browns everything at the back and nothing at the front regardless of shelf, or that has changed its behavior in a fortnight — those are problems. A bake test maps them faster than a thermometer does, and on the electric ovens the pattern usually points straight at an element or its connections. On the gas side it points at the burner, the diffuser, or a door that is no longer being pulled onto its seal.