Thermador Stove Repair in Toronto — Surface element stuck on high

• On a Thermador Pro range the first 'stuck on high / won't simmer' call is almost never a fault: the Star-burner ExtraLow simmer is DESIGNED to cycle the flame fully on and off in the XLO band (at the lowest setting the burner runs about 7 seconds on, 53 seconds off), so a burner that flares then dies, then flares again, is the feature working. We confirm the knob is actually within the ExtraLow band and demonstrate the cycle before condemning a single part. This is the same ExtraLow education the brand is built around, and it ends a real share of these calls with no charge.
• When a Thermador burner genuinely will not drop below medium-high, the heart of the ExtraLow circuit is the burner potentiometer 00422748 (supersedes the discontinued 189816, cross-refs AP3782975) behind each knob. It is wired to work ONLY in concert with the Simmer Control kit 00497234 (two 00422748 pots plus the 00422882 / AP3672574 control unit it ships with) - neither pot works independently. A pot that has lost its taper holds the burner at a high duty cycle, so we meter the pot/simmer-control pair and replace the matched set, not a lone pot, because mixing a new pot with a tired control just re-creates the stuck-high symptom.
• The Simmer Control unit inside kit 00497234 (BSH 00422882, cross-ref AP3672574) is the sealed brain of ExtraLow - its electronics are potted in epoxy, so it is a replace-not-repair part and is now largely discontinued/superseded in the BSH catalogue. When the pots test good but the burner still ignores the low end, the control unit is the fault. We source the current-supersession control before booking the second visit, because a stranded 00497234 on a Pro Harmony is exactly the kind of dealer-order delay we quote up front rather than discover on site.
• A gas burner that lights fine on high but flat-out refuses ExtraLow simmer - flame extinguishes below medium-low even with correct supply pressure - points at the burner BYPASS VALVE seized closed or fouled with boil-over debris, not the electronics. The bypass passage sets the minimum simmer flame; when it gums up the burner has only a high state. We clean/free the bypass and verify the orifice/spud before throwing pot or simmer-control parts at it, since a debris-blocked bypass mimics a dead 00422748 perfectly.
• Flames too high on EVERY burner (not one) on a Toronto Thermador is the gas-conversion mismatch, and it is a safety stop, not a parts call: the range was run on natural gas with LP orifices still fitted, or the pressure regulator cap is on the wrong NG/LP setting. Thermador ships the conversion kit (regulator pin + brass surface-burner orifices/spuds, removed with a 9/32 / 7 mm nut driver). We verify the regulator cap marking (NG vs LP) and that the correct spuds are installed against the rating plate before touching a control - wrong orifice = oversized flame regardless of knob.
• One-burner flame too high with a roaring/lifting flame is often a displaced burner cap or a cracked/loose surface burner tube 00189023 (the brass venturi tube carrying gas from the jet to the burner head), letting raw gas bypass proper aeration. We reseat the cap to its locating pins and inspect/replace the 00189023 tube before assuming a control fault, because a misaligned cap throws an oversized flame the homeowner reads as 'stuck on high.'
• On Thermador's ELECTRIC and induction cooktops, an element that stays full-on regardless of knob is a different platform fault: the infinite switch (simmerstat) has welded its contacts closed and feeds the element 100% duty cycle, or - on touch/induction tops - a relay/power-module that has stuck closed keeps the coil powered. A touch-panel F24 ('touch input key stuck' - a stuck, shorted, or held touch contact) can lock the surface in a fixed state and read as 'stuck on,' so we isolate UI fault from a welded switch/relay: meter the infinite switch for continuity in OFF before condemning the power board, and never parts-cannon the costlier relay/power module first.

Thermador surface element stuck on high in Toronto — the local specifics

• The recurring Toronto pattern on Thermador 'stuck on high' is that the call splits before any part is touched: a large share are ExtraLow working as designed (the flame is supposed to cycle, and we demonstrate it and leave with no charge), and a second cluster are gas-conversion installs where LP spuds or a mis-set NG/LP regulator cap - not a control failure - are oversizing the flame. The genuine parts faults that remain concentrate on the 00422748 potentiometer / 00497234 simmer-control pair on gas Pro ranges and a welded infinite switch or stuck power relay on the electric/induction tops.
• We roll to these calls carrying the matched ExtraLow set - 00422748 burner potentiometers with the 00497234 Simmer Control kit (00422882 / AP3672574 control unit) - plus a 9/32 / 7 mm nut driver and the NG/LP orifice spuds for on-the-spot conversion verification, surface burner tube 00189023 and spare burner caps for the single-burner roaring-flame case, and an infinite switch / meter set for the electric and induction stuck-element variant.

For the full Thermador stove module — every fault, part number and code — see Thermador stove repair in Toronto, and for the same fault across all brands the stove surface element stuck on high guide.