# Node-RED Lost Connection to PLC

**URL:** <https://discourse.nodered.org/t/node-red-lost-connection-to-plc/101379>\
**Category:** General\
**Created:** [29 June 2026 16:59 UTC](https://discourse.nodered.org/t/node-red-lost-connection-to-plc/101379 "2026-06-29T16:59:27Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![dNode12](https://avatars.discourse-cdn.com/v4/letter/d/76d3ee/32.png) [@dNode12](https://discourse.nodered.org/u/dNode12)\
**Post date:** [29 June 2026 16:59 UTC](https://discourse.nodered.org/t/node-red-lost-connection-to-plc/101379/1 "2026-06-29T16:59:27Z")

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Hello,

I'm looking for some help troubleshooting a PLC connection issue.

I'm using the **node-red-contrib-cip-st-ethernet-ip** nodes to communicate with an **Allen-Bradley ControlLogix L83 PLC**. The connection has been working reliably for about a month, but today the PLC connection node suddenly started showing **Offline**.

Here are a few things I've checked:

- I can successfully ping the PLC's IP address from the PC running Node-RED.

- No configuration changes have been made on the PLC.

- The PLC is still running normally and controlling the process.

- The only issue is that Node-RED can no longer establish a connection to it.

I'm trying to figure out what could cause this behavior and where I should start troubleshooting. Has anyone experienced something similar or have suggestions on what to check next?

Any advice would be greatly appreciated. Thanks!

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**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [29 June 2026 17:21 UTC](https://discourse.nodered.org/t/node-red-lost-connection-to-plc/101379/2 "2026-06-29T17:21:22Z")

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What do you see in the node red log?

Have you tried restarting node red and the plc?

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<div class="post-metadata">

**Author:** ![dNode12](https://avatars.discourse-cdn.com/v4/letter/d/76d3ee/32.png) [@dNode12](https://discourse.nodered.org/u/dNode12)\
**Post date:** [29 June 2026 17:27 UTC](https://discourse.nodered.org/t/node-red-lost-connection-to-plc/101379/3 "2026-06-29T17:27:36Z")

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This is the message I see in the Node-RED debug pane:

**"Error communicating with the PLC: Error: TIMEOUT occurred while attempting to establish TCP connection with Controller."**

Yes, I have already restarted Node-RED and power-cycled the PLC

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**Author:** ![vitormnm](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/vitormnm/32/52166_2.png) [@vitormnm](https://discourse.nodered.org/u/vitormnm)\
**Post date:** [29 June 2026 22:25 UTC](https://discourse.nodered.org/t/node-red-lost-connection-to-plc/101379/4 "2026-06-29T22:25:03Z")

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Do all the tags you are reading exist in the PLC?

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**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [27 September 2026 22:25 UTC](https://discourse.nodered.org/t/node-red-lost-connection-to-plc/101379/5 "2026-09-27T22:25:12Z")

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