PID rex c100 error solutions

Hi, today we turned on our injection machine and the measured temperature showed 999°C. We tried to change thermocouple. Nothing happened. Turned it off & on again. No change. And then we tried this:
1. Set your desired temperature to 999.
2. Wait for approx. 30sec
3. PID turns rellay on and off two times.
4. The 999 reading changes to normal one.
5. Party like hell.

We don’t know but it could have happened because of faulty thermocouple which somehow reset the PID.

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The rex c100 is not that reliable.  The sestos is better but costs more.