7890GC oven heat control

[EnvironLab]

I've got a problem with a 7890GC that has me totally baffled. The oven heating elements will continue heating even when the temperature setting is set to cool. The oven will rise in temperature until the "other" half of the instrument realizes its getting too warm and the oven flaps fully open and the fan kicks on high. The fan and the heating elements continually fight each other eventually stabilizing at about 57C. Checking the air coming out of the back, it feels like an accurate reading with a lot of hot air getting blown out. And inlet and detector temps are cool btw. I talked to Agilent. Their first recommendation was to replace the AC power board. I did this and the problem continued. Their next suggestion was to replace the triac and analog power board. Did that and no change. Then they suggested the logic board. Just now put it in and still no change. As far as I know, everything having to do with heater control of the oven has been swapped out. The only things left in the entire circuit would be the heater shroud itself and the cabling. But it seems unlikely that the heating elements, or the cabling for that matter, would continue to somehow draw power on their own, independant of the controllers. And like I said, the temp reading seems accurate. The heater will however shutoff if the door is opened or the temperature is set to "Off". So there is some control. I find it hard to believe that the heater shroud would be the issue or that I installed a part with the exact same problem. But don't know what else it could be.

[EnvironLab]

So just to let everyone know, I replaced the heater shroud and that fixed the issue. Why it behaved the way it did, I don't understand. It did look as if the heater wires were possibly shorting on the frame.