# How to troubleshoot "The instrument encountered a thermal coolant error" on the NovaSeq X Series

**Background** The NovaSeq X and X Plus Series of instruments utilize several coolant loops to ensure normal thermal operation of the instrument. Issues with any of these Thermal Loops will typically present as Critical system errors that prevent or stop sequencing runs to ensure the instrument does not become damaged. These issues typically present with the following error message:\
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"Critical System Error: The instrument encountered a thermal coolant error. Please shutdown the instrument and contact Illumina Technical Support".

**Troubleshooting Actions**

1. Contrary to the error statement, **do not** immediately power cycle the instrument.
2. Collect the following Logs depending on error context:
   1. If during a sequencing run, collect the following files:
      1. The Logs.zip file from the /usr/local/illumina/runs/\[RunID]/Logs directory
      2. The entire InstrumentAnalyticsLogs folder in the /usr/local/illumina/runs/\[RUN\_ID] directory
   2. If during initialization or instrument idle, collect the following files:
      1. The entire `novaseq-x-series-control-software` folder in the /usr/local/illumina/logs directory
      2. The entire non\_run folder in the /usr/local/illumina/performance\_analytics\_data/ directory
3. Contact [Illumina Tech Support](https://www.illumina.com/company/contact-us.html) for next steps to troubleshoot this issue.

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| *For any feedback or questions regarding this article (Illumina Knowledge Article #8271), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000008271%20-%20Instrumentation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


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