La Cornue Induction Pan Not Detected: Why the Cooktop Ignores Your Cookware

What the cooktop is actually doing

An induction zone does not turn on because you touched a control; it turns on because it recognizes a suitable pan. Under the glass, a coil sends out a rapidly changing field, and the electronics watch how the field behaves. A magnetic pan base loads the field in a recognizable way and the zone starts to heat. If nothing loads it, or the load looks wrong, the zone stays idle and the display shows the letter U. On a La Cornue cooktop that message means no pan was detected or the pan is unsuitable, and it clears once a suitable pan is placed on the zone. The reference page for the U display message covers the exact wording.

Cookware problems that look like cooktop problems

When a client calls about a pan that is ignored, the cookware explains the issue far more often than the electronics do. Common culprits:

• Copper, aluminium or glass cookware with no magnetic layer in the base.
• Stainless pots whose bases are mostly non-magnetic metal, with only a thin or small magnetic disc.
• A base that is smaller than the marked zone, so too little of it sits over the coil.
• A warped or domed base that rocks on the glass instead of lying flat.
• A pan placed far off the centre ring, especially a narrow saucepan pushed to one side.
• A wet, greasy or sugar-coated base that holds the pan away from the glass.

A short test sequence

1. Hold a small magnet against the underside of the pan. If it clings firmly across the base, the pan is a candidate; if it slides or does not stick, the pan will not work.
2. Centre the pan on the marked ring and make sure it sits flat and does not spin.
3. Dry the base and the glass with a soft cloth.
4. Try the same pan on another zone to see whether the behaviour follows the pan or stays with the zone.
5. Try a second pan you know works on induction. If that one heats, the first pan is the answer.

If both pans are ignored on every zone, the cooktop itself deserves a closer look. If both are ignored on only one zone, that zone’s coil or detection circuit is the suspect. A detailed post on a different symptom, an induction zone not heating, picks up where this one ends.

When it is not the pan

A technician considers a few other explanations once cookware is ruled out. The coil under the glass can open or short, the circuit that senses the load can drift or fail, and the control that tells the zone to start can send a request that never reaches the power stage. A cooktop that was disturbed during a remodel can also show detection trouble when its supply or its internal connectors are not as they should be. The related display message U400 is worth knowing: it means the cooker is incorrectly connected, the control switches off, and the code stays on the display. That is a connection issue rather than a cookware issue, and it is a job for a technician.

Where the problem tends to start in Bay Area kitchens

Custom kitchens in San Francisco townhouses, Marin hillside homes and wine-country estates often mix cookware collected over many years: heavy copper from one era, enamelled cast iron from another, and newer clad pans bought for induction. It is entirely normal for a well-equipped kitchen to hold a pan that works beautifully on gas and is invisible to induction. If the problem began just after a new set of cookware arrived, or after the range was moved or rewired, say so when you book.

What not to do

Do not leave a thin sheet of metal, foil or a trivet between a pan and the glass to trick detection; that can overheat the surface and damage the glass. Do not slide heavy cast iron across the cooktop while testing, since a scratch is permanent. Do not remove the glass, open the cabinet below or reach for a meter. And do not keep tapping the controls hoping the zone will start; a repeating beep or flashing U is simply the cooktop repeating its answer.

When to book a visit

Book when the U message persists with cookware you know is induction-ready, when it appears on one zone and not the others, when it comes and goes with no pattern, or when the display shows anything other than U. Have the full model and serial plate details, a short list of the pans you tried, and the exact message ready. If you are not sure where the plate is, our model number guide shows the usual spots on a range or cooktop.

The work itself is straightforward to describe: a diagnosis first, a written estimate, and no repair without your approval. You can read more on La Cornue induction cooktop repair or browse the induction cooktop lineup, including the CornuFé 90 and CornuFé 110 pages.

A note on bridged and large zones

Some cooktops let two zones work together under one large pan. If your pan straddles the line between two rings and neither is covered well enough, the cooktop may not register it at all. Move it so the base sits clearly over one marked ring, and read the control instructions for your cooktop before assuming a fault. A pan that is detected one moment and lost the next, particularly when you slide it, is a sign that coverage is marginal, not that the cooktop has failed.

Also think about what changed recently. New cookware, a cleaner that left a film, a spill that dried on the glass, or work on the kitchen supply all give a technician a useful starting point when you describe them.

Frequently asked questions