With the help of the L&L technician over the phone, he concluded that my L&L JD230 kiln is fine after the following tests, and the problem was due to the shelf touching the pyrometer. I will retry the bisque tomorrow.
Here is two tests to check the elements and the replays on the kiln.
First, the elements. Unplug the cord connecting to the red box from the elements. Check the ohms by inserting the probes of the digital multimeter into each hole of the flat part of the plug tightly. Mine read around 17 ohm, for each plug. If element is broken, it does not register the resistance. I bought this kiln with the heavy duty elements option in 2001, and used for bisque cone 07 only. I bisque roughly 40-50 times a year. So, this have been 400 bisque firing done. According to the technician, my element will be for good for long time.
Second, relays. Turn on the power, and set the kiln to “fast glaze”mode, and turn on. Unplug the same plug, and insert the plug into the socket this time, and read the voltage. I read 235V. This shows the relay is working fine. My friend told me that I can get the relays at the Grainger at reasonable price.
There is very good instruction/ trouble shoot articles available at the L&L website.