the large burner on my kitchenaid cooktop takes forever to heat up and doesn't get as hot as it used to.

Diagnosis

This issue is typically caused by a partial failure of the Infinite Switch (the thermostat assembly behind the control knob) or a degraded heating element. In the KitchenAid KFEG500ESS, the infinite switch uses a bimetal strip to cycle power on and off to maintain a specific temperature. When the internal contacts pit or carbonize, the switch may fail to deliver full voltage to the element, resulting in a "low heat" state regardless of where the knob is turned. This manifests as a burner that eventually gets warm but never reaches a rolling boil or a high sear. Another possibility is a high-resistance connection at the burner terminal. Over time, the heat cycles cause the terminal nuts to expand and contract, which can loosen the connection or create a layer of oxidation. This creates a "bottleneck" for the electrical current, preventing the element from reaching its maximum wattage. You can confirm this by using a multimeter to check for continuity across the element; if the element reads within the standard 12-20 ohms but still doesn't heat, the failure is almost certainly in the switch or the wiring harness.

How to Fix It

To resolve this, you will need to replace the Infinite Switch or tighten the element connections. Ensure you have a replacement switch compatible with the KFEG500ESS model series before starting.

1. Power Down: Completely disconnect the range from the 240V power source. Do not rely on the control panel buttons; pull the plug or flip the circuit breaker.
2. Access the Cooktop: Remove the burner grates and any removable drip pans. Locate the mounting screws at the front and rear of the cooktop assembly. Use a socket wrench to remove these screws. Carefully lift the cooktop surface. Because the glass and steel assembly is heavy, prop it up with a wooden block or a sturdy box to avoid bending the frame or cracking the glass.
3. Identify the Switch: Locate the infinite switch corresponding to the large burner. It is the square plastic component connected to the control knob shaft. Note the exact position of the wires.
4. Disconnect and Replace: Use needle-nose pliers to carefully pull the female spade connectors off the switch terminals. Do not pull by the wire; pull by the metal connector. Remove the mounting screws holding the switch to the chassis and slide the old unit out.
5. Install New Switch: Slide the new switch into place and secure the mounting screws. Attach the wires to the terminals in the exact order they were removed. Ensure the connections are tight; a loose spade connector will arc and burn out the new switch.
6. Test Connections: While the cooktop is lifted, check the two wires connecting to the large burner element. Ensure the nuts are tightened firmly with a 1/4" nut driver. If there is visible charring on the wire insulation, trim the burnt section and crimp on a new high-temperature terminal.
7. Reassemble: Lower the cooktop assembly back into place and replace the mounting screws. Reconnect the power and test the burner on the 'High' setting.

If That Didn't Work

• Replace the Heating Element: If the switch is new and the connections are tight but the heat is still low, the internal resistive coil of the burner element may have partially failed or developed a "cold spot." Replace the element assembly entirely. Ensure the new element is seated flush against the cooktop surface to prevent heat loss.
• Check the Main Power Supply: If multiple burners are underperforming, you may have a dropped leg of power coming from your 240V circuit. Use a multimeter to test the voltage at the main terminal block. You should see approximately 120V from each leg to ground and 240V across both legs. If one leg is dead, the burners will operate on 120V, which significantly reduces their heating capacity.
• Inspect the Wiring Harness: Look for "pinched" wires or melted insulation along the path from the switch to the burner. A partial short to ground can bleed off current, preventing the element from reaching full temperature.
• Verify Knob Alignment: Ensure the plastic knob is fully seated on the switch shaft. If the knob is slipping or not fully engaged, you may be turning the knob to 'High' while the actual switch shaft is only turned to 'Medium'.

Heads Up

• Avoid Over-tightening: When securing the burner element nuts, tighten them firmly but do not over-torque them, as this can crack the ceramic insulation of the element.
• Avoid "Quick Fix" Cleaning: Never spray liquid degreasers directly into the control knobs; the fluid can seep into the infinite switch and cause the internal bimetal strip to stick or corrode.
• Voltage Warning: Always use a non-contact voltage tester to confirm the unit is dead before touching any internal wiring, even after unplugging.
• Component Matching: Always verify the part number on the old switch before ordering; KitchenAid often uses different switch ratings for the small vs. large burners.