Thermador Cooktop Not Igniting: Star Burner and Induction Diagnosis
Quick answer
A Thermador Star Burner that clicks but won't ignite is most often caused by moisture in the burner electrode well or debris packed into the star-shaped burner slots. Dry the cooktop thoroughly, clean the burner slots with a toothbrush, and ensure the burner cap is seated flat — these three steps resolve the majority of Star Burner ignition failures. On Thermador induction cooktops, a zone that won't heat typically signals a control-lock activation, an unsupported pan, or an E15/E20 overtemperature fault.
Thermador cooktops are found in two distinct architectures — the gas Star Burner, used in ProHarmony (PCG), ProGrand (PRG), and Masterpiece (SGSX/SGDX) series, and the induction platform, used in Freedom® (CIT/CI) and Masterpiece Induction series. The Star Burner's five-pointed design delivers more even flame distribution than standard ring burners but requires all five burner slots to be clear for the gas to flow and ignite. The induction platform, sourced from Bosch-Siemens, uses zone-specific IGBT inverters and a common control board. Ignition failures on both platforms are usually operator-clearable — but a spark module or IGBT failure requires a specialist.
1. Dry the electrode and clean the Star Burner — the most common fix
Thermador's Star Burner has five radial slots around a center electrode. Moisture from boilover, cleaning, or high kitchen humidity collects in the electrode well and prevents the high-voltage spark from bridging to the burner cap. To diagnose: remove the burner grate and lift the burner cap off — it is not threaded, just resting in place. Dry the ceramic electrode tip and its well with a lint-free cloth, then let it air for 10–15 minutes. Use a dry toothbrush or wooden skewer to clear all five star-shaped slots in the burner head; packed debris blocks gas flow even when the spark fires correctly. Reseat the burner cap flat — a cap tilted even 2–3 mm on one side disrupts the spark-to-cap gap and the burner will click without lighting. On ProHarmony and ProGrand models the grate legs rest in rubber feet; check that the grate is fully seated so the burner cap is level under the grate opening. After cleaning, turn the knob to Lite and listen: you should hear a sharp click followed by a flame within two seconds. If the burner now ignites but extinguishes when you release the Lite position, the thermocouple (a safety shut-off on some models) needs 3–5 seconds of heat before it opens the gas valve — hold Lite slightly longer.
2. Check gas supply and pressure — clicks but no flame at all
If the electrode sparks visibly (you can see the blue spark in a dark room) but no flame appears on any burner, the gas supply is the next check. Confirm that other gas appliances in the home (a wall oven, a separate range) are working; if they are also out, the gas shutoff to the home or the line pressure has dropped — this is a utility issue, not a cooktop fault. If only the cooktop has no flame, find the cooktop's dedicated shutoff valve, usually behind a lower cabinet panel or in the base cabinet below the cooktop cutout, and confirm it is open (handle parallel to the pipe). On dual-fuel ranges with a ProHarmony cooktop top, the cooktop has its own gas valve on the supply line separate from the oven. A partially-closed valve produces a weak, yellow, unstable flame rather than a clean blue flame — open it fully. If the valve is open and gas pressure at other appliances is normal, a faulty gas safety valve inside the cooktop is the likely cause; this requires a specialist.
3. One burner won't spark — igniter switch or spark module
When one burner clicks on all other knobs but not when you turn the non-working knob, the igniter switch for that burner is the most likely cause. Each knob on a Thermador gas cooktop has a push-down igniter switch; when the knob is pushed in to Lite, a small plunger depresses the switch and triggers the spark module to fire that zone's electrode. A failed switch means no spark reaches that burner's electrode — all other burners still click because they have their own switches. Igniter switches on Thermador cooktops (part family 00605508 on ProHarmony / 00602396 on Masterpiece) are behind the burner knob panel and accessible after removing the cooktop from its cutout. If none of the burners spark at all, the spark module (a single board that drives all electrodes) has likely failed; the module is typically mounted at the rear of the cooktop cavity and replaceable as a unit. Never attempt to bypass or short a spark module — replace it with an OEM Thermador part for this voltage class.
4. Induction cooktop: pan detection and E-code diagnosis
Thermador Freedom® induction cooktops use a full-surface induction plane divided into flexible cooking zones. When a zone does not heat: first, check for a control lock indicator (a key icon on the display) — Freedom® cooktops auto-activate the lock after inactivity; hold the lock icon for three seconds to release. Next, verify the pan: induction requires ferromagnetic cookware with a flat base at least 5 inches in diameter; copper, aluminum, glass, and most stainless pans without a magnetic base will not be detected. Place a magnet on the pan bottom — if it holds firmly, the pan is induction-compatible. If the pan is compatible and the zone is unlocked but still does not heat, look for an E15 (overtemperature safety shutdown) or E20 (cooling fan fault) error on the display. E15 is cleared by turning the cooktop off, waiting five minutes for the glass surface to cool, and restarting — it typically occurs after extended high-power use without adequate ventilation clearance below the cooktop. E20 indicates the cooling fan that protects the IGBT inverter has failed; this requires professional diagnosis since the inverter itself may overheat and fail if the cooktop is used with a faulty fan. For F-codes (F10–F30 range) on older Thermador induction models, power-cycle the cooktop by tripping the circuit breaker for 60 seconds — many control board communication faults clear on a full reboot.
5. Persistent ignition failure: IGBT inverter (induction) and spark module (gas)
On Thermador induction cooktops, when one zone heats and an adjacent zone fails with no E-code, the IGBT inverter module for that zone has failed. The Freedom® cooktop uses a segmented inverter board where individual zones can be replaced; older single-board models require full board replacement. IGBT failure on induction cooktops often coincides with using oversized pans that bridge two zones simultaneously — the inverter sees mismatched impedance and overloads one section. On gas models, a spark module that fires all electrodes simultaneously (all burners click when only one knob is turned to Lite) has developed a shorted switch; the cooktop is still usable but the switch should be replaced before the constant firing degrades the module itself. If the spark module fires at random — clicking without any knob turned — moisture has entered the module. Turn off the cooktop, remove the module, air-dry or replace it. Do not leave a gas cooktop with a randomly-clicking spark module unattended.
When to Call a Specialist
Cleaning the Star Burner electrode and slots, reseating a burner cap, checking the gas shutoff valve, and clearing an E15 or control-lock fault are all owner-accessible steps. Gas valve replacement, spark module replacement, and IGBT inverter work require a specialist — the voltages in a Thermador induction IGBT circuit are hazardous, and gas valve work on an installed cooktop has safety implications. We service Thermador ProHarmony, ProGrand, Masterpiece, and Freedom® cooktops across McLean, Great Falls, Potomac, Chevy Chase, Vienna, Arlington, Falls Church, Fairfax, and all of Northern Virginia and DC. Upfront written estimate before any work begins — 90-day workmanship warranty. Call (571) 571-1664.
Frequently Asked Questions
Why won't my Thermador Star Burner light?
The Star Burner's five-slot design is its strength and its most common failure point: any single clogged slot blocks gas flow and the burner won't sustain a flame even with a good spark. Remove the burner cap, dry the ceramic electrode with a cloth, and use a toothbrush to clear all five star slots in the burner head. Reseat the cap flat — a tilted cap (even slightly) breaks the spark-to-cap gap. These three steps fix the majority of Star Burner ignition failures. If the burner sparks but still won't light, check that the gas shutoff valve is fully open and that other gas appliances in the home are working normally.
How much does Thermador cooktop repair cost in Northern Virginia?
Thermador cooktop repair in Northern Virginia typically runs $150–$550 depending on the fault. Burner electrode replacement is $120–$240. Igniter switch replacement (one zone) is $130–$250. Spark module replacement is $180–$380. Gas valve replacement is $250–$500. Induction IGBT inverter replacement is $300–$600 (Freedom® segment) or $350–$700 (single-board models). Control board replacement is $280–$550. We provide an upfront written estimate before any work begins — 90-day workmanship warranty. Call (571) 571-1664.
My Thermador induction cooktop shows E15 — what does it mean?
E15 is Thermador's overtemperature safety code — the glass surface or the internal electronics exceeded the safe operating range and the cooktop shut itself off. Turn the cooktop completely off, wait at least five minutes for the surface to cool, then restart. E15 most commonly occurs after extended high-power use, cooking with lids on at high settings, or when the ventilation clearance below the cooktop cutout is blocked. If E15 recurs immediately after restart, the temperature sensor itself may have failed and requires professional diagnosis.
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