The dual element does not hold at medium heat.

This could be a couple of issues, but unfortunately if it's your element, you would have to replace the entire element, not just the middle part. What's the rest of your model number? I can find a part number for you. (KECD806R****)

I've replied to your other post as well. Please regard that answer :)

SEE PICS Or Oven safety valve needs to be checked with multi meter ohms / voltage
ALSO Test the Burner Heating Element
The stove's burner heating element is a coil of metal sheathed in an insulator. Electrical current travels through the element. Resistance to the passing of electrical current causes the element to heat up. A precise temperature cannot be set for a burner, instead it is turned on and off repeatedly by the control to the achieve an average temperature. When it is set to a low temperature, the element is cycled on and off more frequently. For high temperatures, the heating element is energized longer with fewer on and off cycles. Some burners have two elements, with the second only being used only for high heat settings.
Before testing the heating element, unplug the appliance or shut off the power at the fusebox orbreaker panel to avoid an electrical shock hazard.
When a burner does not heat at all, or only heats up to a lower than expected temperature, the problem is likely to be with the heating element, the temperature control switch, or the wiring. If it only heats at the highest temperature, the problem is with the control or an electrical short, not the burner. If the burner works only intermittently, the problem is likely in the wiring or connectors. To test the heating element, try the following steps.
First, disconnect the heating element from the stovetop. In most cases, this is done by lifting up the burner on the side opposite of the terminals (the part of the burner that disappears under the stovetop). Remove the decorative ring.
Inspect the style of connection. If the burner element has visible blades that fit into the receptacle block, pinch the block with one hand, and pull the heating element free with your other hand. If the terminal block clamps over the element, the housing must be removed and the burner wires disconnected. Unsnap the metal piece or remove the screw that secures the receptacle block and then disconnect the element.
Inspect the heating element. If you find bubbles, warping, or damage to the insulation sheath, the burner must be replaced. If the terminals are dirty or corroded, this can cause poor temperature control, intermittent problems or complete failure to heat. Clean the terminals with steel wool or very fine sand paper to restore good conductivity. Test the resistance of the heating element using a multi meter. Set the multi meter to the ohms setting X1 and touch one probe to each of the terminals. A normal reading is typically somewhere between 20 and 120 ohms. The exact reading differs by manufacturer and mode. If the meter reads infinite resistance or the other extreme of the scale, zero resistance, then the element is damaged and should be replaced. If the measured resistance differs significantly from the expected range, the element is probably bad, but if possible, determine from the manufacturer what the actual resistance should be.
To test for a grounded or shorted element, touch one probe to the surface of the burner and the other probe to each terminal in turn. If you get continui

Element may be bad, check to see if you are getting power to the Element first.

The control you're wiggling (infinite switch)needs replacement. Model# and the position of the dual element (right or left, rear or front) is needed to get the part number.

The elements DO BURN OUT. Replace it.

Often you can see evidence of a hot spot on the element where the final failure occured, but not always.

yes it is your control infinite switch the knob swicht that goes from 1 to 10 or min to max thanks from gilles

as far i know it is normal if u put at high control after a sec,the sencor control is turn off then a sec again it open coz of the sensor, design the sensor for not overheating the hob.it is normal try to position the control in in not a max position.or the pot u use is exactly in the circle or bigger dont put a small one in the bigger hole of ur elctric hob.tnx

sound like you have a shorted element, it will stay hot but not high heat hot (glowing) red, other posibility is bad infinate control switch that switch could be bad

The function 3 element are normal / depend to the intensity adjustment / the small 4th element are set for pre heating w/out burning , try to sdjust in lower adjusment or ann switch for pre heating.