I've a Bosch stovetop and the middle, double burner has been funky since new, won't stay lit after ignition. I assumed it was the thermocouple but replaced it twice. Does this mean I have to replace the control unit itself? I've obviously checked the connections from the thermocouple to the control. Everything looks fine and as I said, this has been a problem since new (12 years ago) but now I can only keep it lit by re-lighting 20 times.