AVCOM, I have worked on a few of the Conceptronic ovens recently for one of my clients. They had a similar issue, all the heaters dropping out with a high temp circuit error which kicks out CON1 (Heater power). If you're saying what I think your saying then there should be a couple of square control boxes in the computer cabinet that make up the redundant high temp monitoring circuit. This circuit is made up of one extra thermocouple mounted in each zone (the 3rd T/C) and these T/C's wires run down and are connected to the back of the boxes. The boxes slide out to allow access to the back of the boxes and there you can see the T/Cs. I believe there are 6 positions, but only 5 are used on the first box and a jumper for the 6th position and then the rest of the T/Cs are on the 2nd box with all non-used T/C positions jumped out. When the oven is turned on, the boxes scan each T/C position one by one as indicated by the lights on the front of the box, and a corresponding readout on the display. When the scan reaches a bad reading it will stop on that position and the box alarm light will be lit and the result is CON 1 gets de-energized. If this is the case either the bad zone overtemp T/C is positioned incorrectly (the T/C tip should be over one of the convection holes and it should not touch the heater plate). Or the T/C is bad, or the control box is faulty. To prove the box is at fault, discount the T/C for the position in question and replace it with a jumper and the controller wil ignore this position. I hope this helps, good luck.