Start with what costs nothing. An electric range runs its elements on 240 volts from a double breaker; if one half trips, the clock, oven light and fan keep running on 120 volts while the elements stay cold. Turn the range breaker fully off, then firmly back on. A gas range needs both gas and a working 120-volt outlet. If the surface burners light, gas is reaching the range, but still confirm the shutoff valve behind it is open, with the handle running along the pipe. Then look at settings. Control lock, a delayed start set by accident, and Sabbath mode, which silences tones and hides display changes, can all pass for a failure, and a showroom or demo mode lets the display and fan work with no heat at all.
On electric ovens the bake element leads the list by a wide margin. Look at it with the oven off and cool: a blister, a split in the sheath or a bright spot where it flared during use means it has burned open. The telltale pattern is an oven that eventually gets close to temperature because the broil element helps during preheat, yet browns the tops of food and leaves the bottoms pale. Hidden-element ovens keep the evidence under the floor panel, so the technician measures instead: a healthy element reads a low resistance, a failed one reads open. Broil elements fail the same way, and on convection ovens the rear element can quit while bake and broil keep working.
For gas ovens, the weak igniter tops the list. The glow bar and the safety valve are wired in series, and the valve opens only when the igniter pulls enough current. An aging igniter still glows bright orange, which convinces most owners it is fine, yet it falls just short of what the valve needs. On a healthy oven the burner usually lights within about a minute and a half of pressing start; a failing igniter stretches that to several minutes, lights only on some tries, or never lights. If the igniter doesn’t glow at all, it has opened completely or isn’t getting power from the control. True safety-valve failures are far less common. A strong rotten-egg smell is a different matter: leave the house without touching switches and call PG&E or 911 from outside.
Further down the list come the controls and the wiring. Relays on the control board switch the bake and broil circuits, and when one burns its contacts the element tests fine but never receives voltage. A temperature sensor that has opened or shorted usually triggers an error code and cuts heating rather than failing silently. A thermal fuse or high-limit switch can open after a self-clean cycle or a cooling fan failure, killing the heat or the whole oven. On gas and electric ranges alike, the connections themselves also fail: a terminal that loosened over years of heating cycles oxidizes, overheats and burns through its wire. That shows up as scorched insulation at the element or igniter connector, and it has to be cut back and repaired along with the part.
