Need help here. I have rising temperature on the left combustion furnace of  Costech EA. It is set at 1020 C but it goes beyond the limit which is 1100C and causes alarm to go on and block everything. All other temperatures are under control, the right furnace and GC column compartment. I replaced the thermocouple, checked and made sure that main power is stable 220-221 V. It still keeps rising beyond the limit, 1100C.
Any suggestions.
Thanks.
Sergei