The short answer
On a Thermador oven, a working broil and a dead bake most often comes down to a weak oven igniter. Thermador pro ranges use sealed burners with electronic ignition, so heat complaints start at ignition and the gas safety valve. The first check below needs no tools, and the list stops where a meter on live terminals begins.
What you observe
- The oven runs but never reaches temperature — Partial heat, which usually means one heat source of two.
- No heat at all while the display works normally — The control is alive and the heat side is not.
- Food browns on one side only — Uneven heat rather than absent heat.
- NEAR MISS — the oven quits partway through the cycle — That is a cycle fault and a different page.
Causes, most likely first on a Thermador oven
- Weak oven igniter — Ranked first here: the igniter on this range both lights the gas and opens the safety valve, so a weak igniter glows beautifully and the oven still never heats.
- Gas supply partly closed — Ranked second: a pro range draws more gas than a standard one, so a partly closed valve that a small burner would tolerate leaves this oven unable to reach temperature.
- One leg of the electrical supply lost — Last on this list: an electric oven lights its display on one leg of the supply and heats on both.
Check in this order, and why
- Watch the igniter and time how long it glows before gas arrives — A long glow with no flame is the signature. First: likeliest cause, least effort.
- Check the shut-off valve behind the range is fully open — Compare burner performance on the cooktop. Second: it separates the next two causes.
- Switch the range breaker fully off and back on — A double breaker can trip on one side only. Third: only once the checks above are clean.
What an owner can safely check
- Watch the burner from a safe distance during a cold start — Glow without flame is the single most useful observation here.
Tools: torchAbout 15 min
- Light a cooktop burner and judge the flame — A weak cooktop flame points at supply rather than the oven.
Tools: noneAbout 10 min
- Cycle the breaker firmly off then on — A standard US household branch circuit is 15 A or 20 A at 120 V; a large appliance circuit is typically 30 A or higher at 240 V.
Tools: noneAbout 5 min
- STOP HERE if the next step needs a meter on live terminals — That is where an owner check ends and a service call begins.
Before you open anything
Safety
Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off.
When to call a technician
Call once the setting, the door and the sensor have all been cleared and the fault is unchanged, because the next tests are on live terminals at a high-current circuit. Call immediately if you smell gas, if the cabinet or the wall behind it is hot, or if the appliance trips its breaker — none of those are things to retry.
Nearest pages of this class
What this page does not cover
This page covers Thermador ovens as a class, not one family or model line. It reasons from how Thermador builds this appliance — enough to rank the causes, not enough for wiring colours, torque figures or part numbers, which differ by family. Where a model-specific page exists it is linked here and is the better answer; this class page has no such child yet, so nothing is withheld by omission.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
