Induction Unit Loses Pan Detection Mid Cook Decision Tree

Why this matters

An induction cooktop that detects a pan correctly at startup and loses detection 5 to 20 minutes into a cook is a focused symptom that points at thermal drift in the pan-sense circuit, a deteriorating pan (carbon steel cookware that has warped and lifted off the glass), or a marginal IGBT driver that derates under load and self-protects. Each branch is a different fix. Tossing a "the customer's pans are bad" answer at every induction call burns the relationship with high-end customers (Wolf, Thermador, Bosch Benchmark, Miele) who paid a premium for the unit and the pans. The tree below uses a known-good test pan to separate cookware faults from unit faults.

Symptom presentation

Customer reports a burner working initially and then turning off with the pan-detect indicator (typically a flashing "PA" or pan-shaped icon on Bosch / Thermador / Miele platforms). Sometimes the burner reduces to a low power state instead of off. The customer often reports the issue is "random" or "happens with some pans, not others."

Confirm with a controlled cook: place a known-good ferromagnetic test pan (a cast-iron skillet or a manufacturer-supplied test pan) with 1 quart of water on the suspect burner. Set to medium power. Time how long until the unit drops detection or reduces power. If the unit holds detection for 30 minutes with the test pan, the customer's cookware is the problem. If the unit drops detection or reduces power with the test pan, the unit is the problem.

Quick checks at the door

Confirm the suspect pan is ferromagnetic by touching a magnet to the bottom. Stainless steel pans must have a magnetic stainless layer in the base; copper and aluminum without ferromagnetic plating do not work on induction. Carbon steel and cast iron work.

Inspect the pan bottom for flatness. A warped pan that has developed a convex bottom lifts off the glass under heat (the pan expands and bows). The induction coil senses no metal in close coupling and drops detection. This is the most common cause when "some pans work and some do not."

Inspect the glass top for chips, cracks, or burn marks. Damage to the coil cover does not directly affect pan detection unless the glass has separated from the substrate.

Pull the unit out and inspect ventilation. Induction cooktops require clearance below for IGBT cooling; an installation that has restricted under-cabinet air flow allows the IGBT temperature to climb, the unit derates, and detection drops mid-cook. Confirm clearance per the manufacturer's installation manual.

Isolation tree

Branch A: known-good test pan holds detection on the suspect burner for 30 minutes. Customer's cookware is the cause. Inspect the customer's pans for flatness and ferromagnetic content. Recommend replacement of failed pans. Document with photographs of the warped bottoms.

Branch B: test pan loses detection on the suspect burner but holds detection on a different burner. The fault is on the burner's specific coil or IGBT driver. Pull the cooktop, inspect the coil for visible damage, inspect the IGBT driver board for the failing burner. Replace the coil or the driver board per the model service procedure.

Branch C: test pan loses detection after a documented run time (for example, 10 minutes), and the same pattern repeats on multiple burners. The control board's pan-sense oscillator is failing under load or the under-cabinet ventilation has been restricted by a retrofit installation. Confirm ventilation first, then test the main board pan-sense voltage at a service point per the model service manual. Replace the control board if board is at fault.

Branch D: test pan loses detection and the unit displays a thermal warning (typically "F-" plus a number, where the number maps to a temperature-zone fault on Bosch / Thermador / Miele platforms). Confirm IGBT heatsink airflow, replace the cooling fan if failed, confirm ambient air temperature at the under-cabinet level.

Branch E: test pan loses detection and the unit returns no warning at all but the burner displays low power. The unit has derated for self-protection and the customer-facing display has not been updated by the firmware. Check for a manufacturer firmware update on platforms that support it (some Thermador, Bosch Benchmark, and Miele units accept firmware updates via service connector).

Branch F: the customer has placed the pan on the burner with a magnetic trivet or a pan holder between pan and glass. Trivets used on cooktops break pan-sense coupling. Educate.

Confirming the diagnosis

After repair, run a full cook test: place 2 quarts of water in the test pan, set to high power, bring to boil, then reduce to low power and hold for 30 minutes. The unit must hold detection at all power levels without dropping.

For Branch A, document the customer pans that failed and the test pan that passed; the customer should understand the failure path.

For Branch B and C, run all four burners through the same test sequentially and confirm consistent behavior across all four.

For Branch D, monitor IGBT temperature with a non-contact thermometer at the heatsink during the test and confirm temperatures stay within the manufacturer's specified maximum.

Remediation parts list by branch

Branch A: no parts; cookware replacement is customer purchase.

Branch B: induction coil for the affected burner, IGBT driver board for the affected zone.

Branch C: main control board, ventilation correction (installation work).

Branch D: cooling fan, ventilation correction.

Branch E: firmware update, main control board if firmware does not clear the issue.

Branch F: no parts; customer education.

When to escalate

If the cooktop is a built-in into a millwork installation that violates the manufacturer's ventilation requirements, the repair is incomplete without an installation correction. Document the violation, photograph the under-cabinet clearance, and refer the customer to a kitchen specialist for the millwork modification. Returning the unit to service in a non-conforming installation will produce a repeat callback and may void the unit warranty.

For units with documented multi-zone IGBT failure, the cost of repair on platforms like Wolf, Thermador, and Miele Benchmark induction can approach replacement of the unit. Have the buy-vs-fix conversation in writing with the customer using model age, repair cost, and replacement-unit DOE efficiency tier so the decision is dollar-anchored.

References

• ANSI / UL 858 (Household Electric Ranges).
• IEC 60335-2-6 (Particular Requirements for Stationary Cooking Ranges, Hobs, Ovens and Similar Appliances).
• DOE 10 CFR Part 430, Subpart B, Appendix I1.
• Bosch / Thermador / Miele / Wolf induction service manuals (under-cabinet ventilation, IGBT thermal specs, service-mode entry).
• NEC Article 422 (Appliance branch-circuit and conductor requirements).