Resolving KTP600 HMI-PLC Communication Failure After IP Change

Problem Description

A field-typical fault condition occurs after an engineer physically changes the IP address of a SIMATIC S7 PLC (S7-1200 or S7-1500) and the connected SIMATIC HMI panel (typically a KTP600 Basic) directly on the device. The PLC is reachable from the TIA Portal project tree, and the HMI can be reconfigured via the Control Panel of the panel itself, but the integrated HMI connection in the engineering project still references the original PLC IP address. As a result, the runtime on the HMI cannot resolve the S7 communication partner, the HMI shows a "Connection failure" or "PLC not reachable" alarm, and tag updates stop.

This symptom is one of the most common startup issues on retrofit and machine-copy projects. It is independent of the firmware of the S7 CPU but is strongly dependent on the panel generation and the panel image version loaded on the HMI. Engineers who attempt to fix the issue exclusively on the HMI side are misled by the assumption that the panel "knows" which PLC to talk to, when in fact the HMI connection is a configured object inside the TIA Portal project, not a discovery protocol.

Affected Hardware and Software

The image version of the Basic Panel is the single most important parameter that determines the available on-device workflow. Panels shipped with image version V13.0.0.0 or newer expose a Control Panel page that allows editing the S7 connection parameters directly. Panels with image V12 or older do not expose this editor and require the TIA Portal project to be the only source of truth.

Root Cause Analysis

The HMI connection in a TIA Portal project is a software object that exists in two synchronized but independent places:

1. The TIA Portal project (engineering side): Located in Project tree → Devices & Networks → HMI_1 → Connections. This object contains the partner IP, slot, rack, and connection name. It is downloaded with the rest of the HMI image.
2. The HMI runtime image (device side): The compiled connection table stored in the HMI flash. The runtime uses this table to open S7 connections to the configured partner IP.

When the engineer changes the PLC IP using any of the following methods without reloading the HMI connection, only the PLC's IP is updated, but the HMI runtime image continues to use the old partner IP that was compiled into the connection table at the time of the last download:

• Editing the PLC IP online in the TIA Portal project (Devices & Networks → PLC → Properties → Ethernet addresses → IP address) and downloading only the PLC.
• Editing the PLC IP through the CPU Web Server of the S7-1200/S7-1500.
• Using a SIMATIC Automation Tool to push a new IP to the PLC.
• Using a third-party tool such as Proneta to set the IP.

The HMI's own IP address is independently managed. Setting the HMI's Control Panel → Network & Dial-up Connections → PN/IE → Properties → IP address only updates the device-side IP. The HMI connection table continues to point to the previously configured PLC IP until a recompile and download is performed.

The reverse case is also common: the engineer changes the HMI's IP on the panel or in the project and downloads the HMI, but forgets that the HMI connection's "Partner" field is the PLC IP, not the HMI IP. The Properties dialog in TIA Portal exposes both, and confusing them is the most frequent cause of this support case.

Verification of Symptoms Before Repair

Before editing the project, confirm the actual communication state from the panel itself. This avoids spending hours editing the wrong object.

1. On the KTP600, open Control Panel → Network & Dial-up Connections → PN/IE and note the IP address. This is the HMI's own address.
2. From the same Control Panel, navigate to the System → Network or S7 Connection Diagnostics page (available on image V13+). Confirm the configured partner IP and connection status.
3. On a PG/PC connected to the same subnet, run ping <PLC IP> to verify the PLC is reachable at its new address.
4. From the PG/PC, attempt an S7 connection using the TIA Portal Online → Accessible devices function. If the PLC shows up, the network path is intact; the problem is purely in the HMI connection object.
5. On the HMI, look at the status bar at the bottom of the runtime. A red connection icon, the message "Connection to PLC disrupted," or a flashing "PLC: --- " indicates a failed connection.

Solution A — 1st Generation Basic Panels (Image V12 and Older)

This is the canonical workflow for the panel in the source case. The on-panel editing of the S7 connection is not available, so all changes must originate in the TIA Portal project.

Prerequisites

• TIA Portal V13 SP1 or later (must match the project version, e.g., V15.1 for projects created in V15.1).
• The original project file (.ap13, .ap14, .ap15, .ap15.1, .ap16, .ap17, .ap18) with the HMI device and the HMI connection intact.
• Ethernet cable between PG/PC and the HMI, or the PG/PC on the same PROFINET subnet.
• The HMI's current IP address (visible on the panel during startup banner or in the Control Panel).

Step-by-Step Procedure

1. Open the project in TIA Portal. In the project tree, expand Devices & Networks.
2. Identify the HMI device node (e.g., HMI_1 / KTP600). Right-click → Properties opens the HMI device configuration.
3. Select the PROFINET interface of the HMI. In Properties → General → Ethernet addresses, set the HMI's own IP address, subnet mask, and (if used) router address. This must match the address currently configured on the panel itself, or you will not be able to download.
4. In the Devices & Networks editor, click the HMI device. The network view shows the HMI's PROFINET port. If a HMI connection has not yet been created, drag a connection line from the HMI's PROFINET port to the PLC's PROFINET port. TIA Portal will offer to create an HMI connection automatically.
5. If the HMI connection already exists, select the connection line. In the inspector window under Properties → General → Connection, locate the partner (PLC) end point settings.
6. Set the Partner IP address field to the new PLC IP. The Partner is always the PLC, not the HMI. The field is labeled differently depending on TIA Portal version:
   • V13: Address details → Partner → IP address
   • V14/V15: Properties → General → Connection → Address details → Partner
   • V15.1 and newer: Properties → General → Connection → Connection path → Partner endpoint → IP address
7. Confirm the Access point is set to S7ONLINE for PROFINET or PN/IE for routing scenarios. For a direct Ethernet link between PG/PC and HMI, the access point must resolve to the correct network adapter.
8. Save the project. Right-click the HMI device → Compile → Software (rebuild all). This regenerates the HMI runtime image with the new connection table.
9. Right-click the HMI device → Download to device → Hardware and software (only changes). If the panel is on a different subnet, select Visible target devices and pick the HMI by its IP/MAC. Confirm the PG/PC interface assignment in the dialog.
10. During download, the HMI restarts. After restart, the new connection is active.

Distinguishing HMI IP vs. Partner IP in the Project Tree

A frequent confusion is selecting "Port interconnection" inside the HMI's PROFINET port properties and trying to enter the PLC's IP there. The Port interconnection editor only handles the topology of PROFINET ports (peer-to-peer cable relationships, port numbers, and the partner port for cable diagnostics), not the HMI connection's partner IP. The correct location for the partner IP is the HMI connection object, not the port.

Solution B — 2nd Generation Basic Panels (Image V13 and Newer)

From image V13.0.0.0 onward, Basic Panels expose a Control Panel editor that allows changing the S7 connection partner IP directly on the device, without a TIA Portal download. This is the recommended path for field service and commissioning engineers who do not have the original project at hand.

1. On the panel, open Control Panel → Network & Dial-up Connections → PN/IE.
2. Confirm the HMI's own IP and subnet mask.
3. Open Control Panel → System → Connections (or WinCC Connection Editor depending on image version).
4. Select the S7 connection that was previously configured (e.g., "Connection_1").
5. Edit the Partner IP address to the new PLC IP. The slot and rack fields stay at their default values (slot 1 for S7-1200/1500).
6. Save the change. The runtime restarts the connection. No project reload is required.

Solution C — Comfort Panels

Comfort Panels (TP700, TP900, TP1200, TP1500, TP1900, TP2200) include a full Start Center and Control Panel with the S7 connection editor. The workflow is identical to Solution B but with a richer diagnostics surface (e.g., the System → Network → Connections view shows the connection state in real time and reports the S7 error code from the PLC side).

Verification

After applying the solution, verify connectivity in three layers.

Common Pitfalls and Field-Notes

• Wrong interface in the PG/PC assignment. The PG/PC must use the same physical adapter that reaches the HMI. With multiple NICs (e.g., a wireless adapter and a wired PROFINET adapter), TIA Portal may try to route through the wrong interface and report "Device not reachable." Use Online → Accessible devices to force the interface selection.
• Subnet mismatch. The HMI's subnet mask and the PLC's subnet mask must agree on the network portion of the address. Mixing 255.255.255.0 and 255.255.254.0 between the two devices is a silent failure that lets ping succeed but blocks the S7 connection establishment.
• Routing through a managed switch with PROFINET priority disabled. The HMI/PLC S7 connection is unicast UDP. If the switch's MAC table has aged out the PLC's MAC after the IP change, the first few connection attempts may fail. Wait one MAC aging interval (typically 5 minutes) or power-cycle the switch.
• Project version mismatch. Downloading a project compiled in TIA Portal V15.1 onto a panel that has an image compiled for V14 results in a download error. Match the TIA Portal version to the image version of the panel.
• Active runtime blocking the download. The HMI runtime must be stopped before download. The panel will prompt automatically. If the prompt is dismissed accidentally, manually close the runtime from the Control Panel before retrying.
• Firewall on the PG/PC. Windows Firewall can block ISO-on-TCP port 102 used by S7 communication. Allow the TIA Portal process (s7oiehs64.exe) through the firewall during commissioning.
• Multiple HMI connections in the same project. If the project has more than one HMI, each one has its own HMI connection object. Editing the wrong one is easy. Verify the connection by its name in Devices & Networks.

Diagnostic S7 Error Codes on the HMI Side

When the HMI cannot establish the S7 connection, the runtime logs an error code in the HMI log file. The most common codes for this failure mode are listed below. These are reported on Comfort Panels and on Basic Panels 2nd Generation with image V14+.

These codes are visible in the HMI log under Control Panel → System → Logs on Comfort Panels, and in the runtime alarm buffer on Basic Panels 2nd Generation.

Related Configuration in TIA Portal

Beyond the IP change, several adjacent settings can break HMI/PLC communication if misconfigured. Audit each one during commissioning.

PLC Connection Resources

An S7-1200 CPU (firmware V4) supports a maximum of 16 S7 connections. An S7-1500 supports 64. Each HMI, PG/PC, and OPC UA consumer consumes one or more. When the limit is reached, new connection requests are rejected with HMI error 0x0011. Raise the maximum in CPU Properties → Communication → Connection resources.

Access Permissions in the PLC

The HMI's connection to the PLC uses the configured access level. If the PLC is set to "Complete protection" without a password, the HMI connection is rejected. Verify in CPU Properties → Security → Access level. The recommended default for production is "Full access (no protection)" for the HMI connection and a separate password for the PG/PC connection.

PG/PC Interface Assignment

The Set PG/PC Interface tool (Start → Siemens Automation → Set PG/PC Interface) controls which network adapter is used for the S7ONLINE access point. A wrong selection causes "Accessible devices" to find the PLC but the HMI download to fail.

Preventive Measures for Future Commissioning

• Store the TIA Portal project in a version-controlled repository (e.g., Git LFS) so the original connection configuration is recoverable.
• Document the network plan (HMI IP, PLC IP, subnet mask, gateway, slot, rack) inside the project documentation or as a comment in the HMI connection properties.
• For every IP change, perform a full HMI download (not just a PLC download) to keep the connection table synchronized.
• Use SIMATIC Automation Tool or PRONETA to push IP changes that include a verification ping afterward, so the engineer confirms the new address is live before troubleshooting the HMI side.
• For service access without the original project, equip 2nd Generation Basic Panels or Comfort Panels and document the on-panel connection editor procedure in the operator manual.

FAQ