my oven takes way longer to preheat than it says, like 30 minutes to hit 350.

Diagnosis

The sluggish preheat time on your Whirlpool WFE515S0JS is typically caused by a "partial failure" of the bake element or a drifting oven temperature sensor (RTD). Unlike a total burnout where the element stays cold, a partial failure occurs when the internal resistive wire develops micro-fractures or oxidation. This increases the electrical resistance, meaning the element cannot reach its full wattage and takes significantly longer to radiate heat into the oven cavity. Another common culprit is the oven temperature sensor. If the sensor has "drifted" out of calibration, it may report a temperature higher than the actual internal air temperature. This tricks the control board into thinking the oven has reached 350°F when it is actually only at 250°F, causing the heating cycle to shut off prematurely or cycle on and off too frequently, dragging out the preheat process. You can confirm this by using a standalone oven thermometer placed in the center of the rack; if the display says 350°F but the thermometer reads 300°F, the sensor is the primary failure point.

How to Fix It

To resolve this, you must first isolate whether the failure is electrical (element) or sensory (sensor). Follow these steps precisely:

1. Disconnect the range from the 240V power source by unplugging it from the wall. This is critical as you will be working with live electrical terminals.
2. Remove the oven racks and the bottom heating element cover if applicable. Locate the bake element terminals at the rear of the oven chassis.
3. Using a digital multimeter set to the Ohms (Ω) setting, place the probes on the two terminals of the bake element. A healthy element should read between 20 and 30 ohms. If the reading is "OL" (Open Line) or significantly higher than 40 ohms, the element is failing and must be replaced.
4. If the element tests fine, locate the oven temperature sensor probe (the small metal rod protruding from the back wall of the oven). Remove the two screws holding the sensor bracket and pull the sensor out.
5. Set your multimeter to the 20k ohm scale. Measure the resistance of the sensor at room temperature (approx 70°F). It should read approximately 1080 to 1100 ohms. If the reading is outside this range by more than 50 ohms, the sensor is faulty.
6. Replace the defective part. If replacing the element, ensure the new part is seated firmly in the mounting brackets to prevent "sagging," which can cause uneven heating or contact with the oven floor.

If That Didn't Work

• Check the oven door seal (gasket). Inspect the fiberglass or rubber seal around the perimeter of the door. If there are tears or gaps, heat escapes rapidly, forcing the oven to work twice as hard to reach temperature. Replace the gasket if you can feel heat leaking from the edges during a preheat cycle.
• Inspect the Electronic Range Control (ERC) board for "cold solder joints." Over time, the high heat of the oven can cause the solder on the relay board to crack. This prevents the full 240V from reaching the elements. Visually inspect the back of the control board for any charred areas or loose connections.
• Verify the calibration settings. Sometimes the oven is simply offset. Access the "Calibration" mode by pressing the "Bake" and "Broil" buttons simultaneously (depending on the specific board revision) to adjust the temperature offset by +/- 35 degrees.
• Test the voltage at the element terminals during a heat cycle. Use a caution-protected voltmeter to ensure the board is actually sending 240V to the element. If the board only sends 120V, one side of the dual-pole switch in the control board has failed.

Heads Up

• Avoid using "oven cleaner" on the temperature sensor probe; caustic chemicals can erode the metal and change the sensor's resistance, leading to inaccurate temperature readings.
• When replacing the bake element, always use new high-temperature spade connectors. Reusing old, charred connectors creates high resistance points that can melt the wiring harness.
• Ensure the oven is completely cool before testing the sensor, as resistance changes based on temperature; testing a hot sensor with room-temperature specs will lead to a false diagnosis.
• Periodically check the power cord for signs of melting or discoloration at the wall outlet, as a loose 240V connection can cause voltage drops that affect heating efficiency.