Running Multiple WinCC Runtime Instances on One PC

Overview

Siemens WinCC Runtime is engineered as a single-instance HMI visualization host on a Windows computer. By default, the WinCC flexible Runtime loader enforces a one-runtime-per-PC rule through the OnlyOneInstance flag inside the HmiRTm.ini file. Operators who want to run two or more HMI projects on the same machine (for example, a local machine panel plus a supervisory overview, or two independent production cells) must override that flag and resolve the secondary failure mode that appears as a project file cannot be loaded error when the second .fwx file is opened.

This reference covers the legacy WinCC flexible Runtime configuration path, the role of every parameter in HmiRTm.ini, the standard fix for the fwx-file load failure, and the modern WinCC Unified / WinCC Professional parallel installation approach documented in TIA Portal. The two techniques address different generation products and should be selected based on which HMI engineering suite generated the project.

Prerequisites

• Windows 10/11 Pro or Windows Server 2016/2019/2022 with administrator rights.
• WinCC flexible Runtime 2008 SP5 or higher installed at the default location (%ProgramFiles%\Siemens\Automation\WinCC flexible\WinCC flexible Runtime\) or a custom path.
• Two valid .fwx compiled project files generated by WinCC flexible ES.
• A valid runtime license for each simultaneous project. A single WinCC flexible Runtime license authorizes one project; a second instance requires either a second full license or a coordinated RC license when used as a redundant partner.
• Read/write permission for the runtime installation directory because HmiRTm.ini is owned by the installer and is write-protected under standard user accounts.

HmiRTm.ini File Location and Structure

The HmiRTm.ini file is the central configuration for the WinCC flexible Runtime loader. It lives next to the runtime executable, and its full path is:

A freshly installed runtime contains the following default content:

[configuration]
;LoadConfigFile=PDataDef.fwx

[Application]
ShowSplashWnd=True
OnlyOneInstance=True
SuppressTopMost=True

The two relevant sections are:

The OnlyOneInstance Parameter

The OnlyOneInstance flag is a single-instance guard that the runtime uses to prevent two HmiRTm.exe processes from fighting for the same project file, the same Windows message hooks, and the same licensing slot. The guard is enforced when the second HmiRTm.exe is launched: the loader checks for an existing instance and refuses to start if OnlyOneInstance=True.

To permit parallel projects, change the value to False:

[Application]
ShowSplashWnd=True
OnlyOneInstance=False
SuppressTopMost=True

After saving the file, attempt to start the first runtime by double-clicking its .fwx file, then start the second .fwx file. The two runtimes will launch side by side.

Resolving the fwx-File Load Error

Setting OnlyOneInstance=False is necessary but not always sufficient. A common reported failure mode is:

The fwx-file cannot be loaded.

This error appears when the second runtime cannot resolve the project file path or the LoadConfigFile directive. The following checks address every known cause:

1. Verify the .fwx file is accessible from the second runtime's working directory. The runtime resolves a relative LoadConfigFile entry against the current working directory, not against the HmiRTm.ini location. When you launch the project by double-clicking the .fwx file in Explorer, the working directory is the folder containing the file. When you launch it from a shortcut, the working directory is the shortcut's "Start in" field.
2. Remove the absolute path from a previous installation. If HmiRTm.ini still contains an absolute LoadConfigFile=C:\Some\Path\Project.fwx entry from a prior project, the runtime tries to load that exact file. Comment the line out (prepend ;) and let the runtime pick up the .fwx passed on the command line.
3. Confirm no read-only attribute is set on the .fwx file. WinCC flexible Runtime writes runtime data back into the project folder (alarm logs, tag logs, recipe directories). A read-only file forces the runtime to terminate the load to protect data integrity.
4. Check the project compatibility. A project compiled with a newer ES version cannot be loaded by an older runtime. Verify the runtime version matches the WinCC flexible ES that produced the .fwx.
5. Confirm the second runtime process is launched with administrator rights. Some Windows security policies prevent the second process from binding to message hooks if the first was elevated and the second was not. Both runtimes must run at the same integrity level.
6. Check the license server reachability. If both projects require a license and only one license is available, the second instance may fail to acquire the license and abort during initialization, surfacing as a generic project load error. Use a separate license container for each instance, or use a single license and disable the licensing check in the second runtime for development.

WinCC Unified and WinCC Professional Parallel Installation

For projects engineered in TIA Portal (V17 / V18 / V19 / V20 / V21), the supported method for hosting multiple HMI projects on a single device is the parallel installation of WinCC Unified Runtime and WinCC RT Professional. The Siemens TIA Portal documentation for V21 describes the exact procedure, supported combinations, and licensing boundaries. Reference: Parallel Installation - TIA Portal (V21).

The key points documented for parallel installation are:

• WinCC Unified Runtime and WinCC RT Professional can be installed on the same Windows device provided the TIA Portal installation order follows the documented sequence. Unified must be installed first, Professional second, or both can be installed together as a combined setup.
• Each runtime manages its own project, its own service account, and its own port range. By default, Unified uses 4430 for the Unified Collaboration, 8888 for the runtime web server, and 1344-1345 for OPC UA. Professional uses 135, 445, and a configurable set of WinCC-specific ports. Verify no port collisions exist with other software on the host.
• Each runtime has its own autostart entry. To control which runtime starts with the operating system, disable the corresponding Windows service (WinCCUnifiedRT or CCFastCtrlSrv) per project.
• License assignment is independent. A WinCC Unified RT license covers only Unified projects; a WinCC RT Professional license covers only Professional projects. Running one of each consumes one license from each pool.
• Project files live in separate folders: Unified projects are stored under %ProgramData%\Siemens\Automation\WinCCUnified\RT\<ProjectName>\ while Professional projects are stored under %ProgramFiles%\Siemens\Automation\WinCC\RT\<ProjectName>\. There is no shared project path.

Step-by-Step Configuration Procedure

The procedure below applies to WinCC flexible Runtime. Follow each step in order. After each step, a verification action is included.

1. Stop all running runtimes. Open Task Manager, end every HmiRTm.exe process. Verify: the WinCC flexible Runtime system tray icon disappears.
2. Open the INI file in an editor with administrator rights. Right-click Notepad (or your editor of choice), choose Run as administrator, then open C:\Program Files\Siemens\Automation\WinCC flexible\WinCC flexible Runtime\HmiRTm.ini. Verify: the file opens in read/write mode (Notepad does not show a read-only banner).
3. Locate the [Application] section and change OnlyOneInstance=True to OnlyOneInstance=False. Do not alter the LoadConfigFile line. Save the file. Verify: the file size is non-zero and the modification timestamp updates.
4. Confirm both .fwx project files are on a writable drive. Move the files to C:\HMI\Project1\Project1.fwx and C:\HMI\Project2\Project2.fwx if they are not already. Verify: both files have the read-only attribute cleared (right-click → Properties → Read-only unchecked).
5. Launch the first project. Double-click C:\HMI\Project1\Project1.fwx. The runtime starts, the splash screen displays, and the project screen appears. Verify: HmiRTm.exe is visible in Task Manager with the expected window title.
6. Launch the second project. Double-click C:\HMI\Project2\Project2.fwx. The second runtime starts in a separate window. Verify: two HmiRTm.exe processes are running with distinct window titles and distinct PIDs.
7. Arrange the windows. Use the Windows taskbar preview or right-click the second runtime's system tray icon to set Always on top if one project should remain visible above the other.

Verification and Testing

After both runtimes are running, perform the following functional checks to confirm the multi-instance configuration is stable:

Troubleshooting Matrix

Field-Proven Caveats

• Single-core loader. WinCC flexible Runtime is single-threaded for the screen rendering path. Two heavy projects can saturate a single core. On modern multi-core CPUs, set the process affinity to distinct cores via Task Manager → Details → Set Affinity to balance load.
• Shared global atom table. Older WinCC flexible Runtime versions use Windows global atoms to coordinate with the loader. If one project crashes and leaves stale atoms, the second project may fail to start. Reboot the machine to clear the atom table.
• Display scaling. Two projects with different DPI scaling settings can fight over the system DPI cache. Set both to the same scaling in their Project Properties → Display.
• Antivirus exclusions. Add the runtime installation folder and both project folders to the antivirus exclusion list. Some endpoint protection products block the second HmiRTm.exe as a "suspicious duplicate".
• Remote desktop sessions. If you start the second runtime through a Remote Desktop session while the first is running on the console, the second instance may not acquire the input desktop. Both runtimes must run in the same Windows session (console or RDP, but not mixed).