Fixing WinCC 'No Connection to Data Server' Error with PLC-SIM

Problem Description

A working SIMATIC WinCC (WinCC Explorer, V6/V7) project is connected to a STEP 7 PLC-SIM instance over the S7-ONLINE / TCP / Named Pipe channel. The user can issue operator commands from the WinCC graphics (e.g. set bits, write values) and the values return to the PLC without errors. Tags, including the BOOL/INT/DWORD bits used to drive the alarm logic, are correctly mapped in the WinCC tag management and update with the correct green "connected" state.

However, when the engineer opens the Alarm Control / Alarm View in Graphics Designer and activates the runtime, the status line of the control displays No connection to data server instead of Ready. No incoming alarms are displayed, even though the trigger bit in the PLC has been set. The PLC program, the alarm tags, and the STEP 7 message configuration are all in place.

Error string observed in the WinCC Alarm Control:

Status: No connection to data server
       (or localized equivalent: "Keine Verbindung zum Datenserver" / "Sin conexion al servidor de datos")

This error appears only for the alarm subsystem. The tag subsystem continues to function normally, which is the diagnostic fingerprint of an uninitialized WinCC Server Package, an expired/missing runtime license, or a startup option that was not enabled.

Affected Products and Versions

Component	Versions Known Affected	Minimum Version Validated
SIMATIC WinCC V6 (classic)	V6.0 SP2, V6.2, V6.2 SP2	V6.0 SP3
SIMATIC WinCC V7	V7.0, V7.0 SP1, V7.2, V7.3, V7.4	V7.0 SP3
S7-PLCSIM	V5.4, V5.5 (with STEP 7 V5.4/V5.5)	S7-PLCSIM V5.4 SP5
TIA Portal WinCC (Comfort/Advanced/Professional)	V11, V11 SP2, V12, V13, V13 SP1	V11 SP2 (UD5) and later
Automation License Manager (ALM)	V5.2 and later	V5.3 SP3

Compatibility note: TIA Portal V11 WinCC runtime shows a similar alarm anomaly, but instead of the text No connection to data server it may simply fail silently or post event 12502 in the HMI diagnostics. The root cause is identical: the alarm server component of the runtime has not been started or has not been licensed.

Root Cause Analysis

The No connection to data server state in the WinCC Alarm Control does not indicate a fault in the S7 protocol channel. It indicates that the WinCC Runtime cannot reach the internal Alarm Logging Service (component name CCAlgServer.exe) which owns the message archive, the message classes, and the configured message tags. The Tag Management channel to PLCSIM works because it uses a separate service (CCRTMgr.exe).

Three independent root causes have been observed in field installations and all three produce this exact symptom string:

1. No Server Package generated/loaded – WinCC needs to compile a server package (a binary descriptor of all configured tags, messages, archives) and the Alarm Logging service has to load it before runtime can resolve any message-tag binding.
2. Runtime startup option for Alarm Logging disabled – In WinCC Explorer, the Computer → Startup list has a checkbox for the Alarm Logging service. If it is unchecked, the service never starts and the Alarm Control will report no data server.
3. Missing/expired WinCC Runtime License – The WinCC basic runtime license covers tag communication, but the alarm subsystem additionally requires either a WinCC RC (Runtime + Configuration) license or a WinCC RT (Runtime only) with the alarm feature bit enabled. If the license is missing, expired, or not visible to the ALM, Alarm Logging enters degraded mode.

The same three causes are valid for TIA Portal V11+ WinCC (Comfort/Advanced panels and PC Runtime) – the only difference is the user interface where the start-up list is located.

Diagnostic Checklist

Run these checks in order before changing any project configuration. Each one takes less than a minute and eliminates one root cause.

1. Verify that the basic tag channel works. Open Graphics Designer, add an I/O Field bound to a process tag, switch to runtime, and confirm the value updates. If this is green, the S7 channel to PLCSIM is healthy and the problem is isolated to the alarm subsystem.
2. Inspect the Alarm Control status string. It must read No connection to data server or a localized equivalent. Any other error string (e.g. No connection to server, Connection failed) indicates a different fault and the rest of this article does not apply.
3. Open the WinCC Explorer left tree → Server. Note whether the entry is empty, has a red X, or is populated. The Server node is the diagnostic anchor for the next two solutions.
4. Open WinCC Explorer → Computer → Startup. Confirm that Alarm Logging (and ideally Tag Logging if you intend to use archives) are listed and the Active column is checked.
5. Open the Automation License Manager (Start → SIMATIC → Automation License Manager). Confirm that a valid WinCC RC or RT license is on the local license container (local drive, USB dongle, or network server). An expired or detached license must be repaired before the alarm server will start.
6. Check the Windows services. WinCC Alarm Logging (display name SIMATIC WinCC AlarmLogging) must exist and be set to Automatic. If the service is set to Disabled, the alarm server cannot start regardless of project configuration.

Solution 1: Generate and Load the Server Package

This is the most common fix and resolves the problem in the majority of WinCC V6/V7 installations where the user has only configured tag communication but never executed a server-package compilation.

Step-by-step

1. Close any running WinCC Runtime instance (right-click the WinCC icon in the system tray → Exit WinCC Runtime).
2. In WinCC Explorer, expand the left navigation tree and locate the Server node directly under the computer name.
3. Right-click Server and select Load Server Package… from the context menu. (In older V6 installations the entry reads Generate Server Package; the result is identical.)
4. A file dialog opens pointing to the project directory. The default location is <ProjectName>\<ComputerName>\Packages. The package file is named <ComputerName>_<Timestamp>.pck for V6 or <ProjectName>.srtp for V7.
5. If WinCC prompts that the package does not exist and asks to generate it, click Yes. WinCC will compile all messages, tags, archives, and graphics references into a single binary.
6. Wait for the generation to complete. A green check icon appears next to the Server node when the package is valid and loaded.
7. Restart WinCC Runtime. In the Alarm Control, the status line must now read Ready instead of No connection to data server.

What the server package actually contains

Content Block	Source in WinCC Explorer	Why Alarm Logging needs it
Tag list (internal + process)	Tag Management	Resolves the trigger address of each message
Message classes / message types	Alarm Logging	Provides the priority, color, and acknowledge rules
Message tags (text tags, process values)	Alarm Logging → Message → Properties	Binds the configured {<TagName>} placeholders in the message text
User archives (optional)	User Archives	Needed only if message text references archive fields
Time settings / time zones	Computer → Time Settings	Determines how timestamps in the alarm list are displayed

Why re-generating is sometimes required after edits: the server package is a snapshot. If you add a new alarm tag, change a message text, or modify the trigger address of a message in the WinCC Explorer while the runtime is closed, the package on disk becomes stale. WinCC will detect this at the next runtime start and post a warning in the WinCC diagnosis window; the fix is to repeat steps 3–5 above. Many users forget this and are puzzled that the alarm control worked once and then stopped working after a tag change.

Solution 2: Enable Alarm Logging in the Startup List

If the server package is generated correctly but the alarm server still does not start, the next most likely cause is that the Alarm Logging service is not flagged for autostart.

1. In WinCC Explorer, open Computer → right-click → Properties → tab Startup.
2. Verify that Alarm Logging is listed and that the Active / Start checkbox is selected.
3. Add or enable these companion services for a healthy alarm environment:
   • Graphics Runtime (mandatory if you run the project from Graphics Designer)
   • Tag Logging Runtime (optional, only if you use tag archives)
   • Report Runtime (optional, only if you trigger shift reports)
   • Redundancy Sync (skip unless you run a redundant pair)
4. Click OK and restart the WinCC Runtime to apply.

Alternative: launch Alarm Logging manually

For quick verification you can start the alarm service from a Windows command line independent of the WinCC project:

net start "SIMATIC WinCC AlarmLogging"

If the service starts cleanly and the Alarm Control status changes to Ready, the service is healthy and the only remaining problem is the WinCC startup list. If the service fails with Error 1053: The service did not respond to the start or control request in a timely fashion, the most common cause is a corrupted database in <Project>\<Computer>\ALG\. In that case stop the service, rename the ALG folder, restart the service, and re-generate the server package – Alarm Logging will rebuild a fresh database.

Solution 3: Repair the WinCC Runtime License

Even with a valid server package and a correctly configured startup list, Alarm Logging will refuse to enter a fully licensed state if the WinCC runtime license is missing or expired. This is enforced by the Automation License Manager (ALM) and the result is identical to the uncompiled-package symptom from the operator's point of view.

1. Close the WinCC Runtime.
2. Open Automation License Manager (Start → SIMATIC → Automation License Manager).
3. Locate the Local License Container (your hard drive) and the Network License Container (the license server, if any). Both are listed in the left tree.
4. Check whether a WinCC license is present, what its type is, and whether it is still valid. The Valid until column is the source of truth.
5. If a license is missing or expired, transfer a valid license from the License Key USB stick or the central server using the ALM context menu → Transfer License.
6. Reboot the WinCC computer if a newly inserted USB dongle is not detected. USB dongles are enumerated late in the boot sequence on some Windows versions and ALM may not see them otherwise.

License type matrix

License	Covers Tag Comm.	Covers Alarm Logging	Typical Use
WinCC Demo	Yes (time-limited)	Yes (time-limited)	Test / training
WinCC RT (Runtime only)	Yes	Yes (with active alarm option)	Production, project designed elsewhere
WinCC RC (Runtime + Configuration)	Yes	Yes	Engineering stations and test rigs
WinCC Client	Yes (client channel)	No server-side logging	Operator stations connecting to a server

Watch out: a WinCC Client license cannot be used to host the Alarm Logging service on a stand-alone PC connected to PLCSIM. To bring a WinCC Alarm Control online against a local PLCSIM you need a WinCC RC or WinCC RT license. Using a Client license on a stand-alone project is one of the most common reasons the alarm subsystem is degraded even when tags work.

Solution 4: TIA Portal V11 / V12 / V13 Specifics

The behavior described in the original case is also reproducible with TIA Portal WinCC. The dialogs are different but the underlying mechanism is identical.

Where to find the equivalents in TIA Portal

Classic WinCC V6/V7 step	TIA Portal V11+ equivalent
Server → Load Server Package	Project tree → <HMI device> → Compile → Software (all)
Computer → Startup list	Project tree → <HMI device> → Runtime settings → Services
Alarm Logging configuration	Project tree → <HMI device> → HMI alarms → Analog / Discrete alarms
Automation License Manager	Automation License Manager (same tool, V5.2+)

Step-by-step for TIA Portal V11+

1. In the TIA Portal project tree, right-click the HMI device and choose Compile → Software (all). This is the equivalent of generating a server package.
2. Open Runtime settings → Services. Enable Alarm Logging for the start sequence of the runtime.
3. Open HMI alarms, confirm that the trigger tag is mapped to a valid PLC tag of the PLCSIM instance, and that the Event (rising edge / falling edge / value range) is configured.
4. Download the HMI project to the WinCC Runtime (PC Runtime or panel).
5. Trigger the alarm bit in PLCSIM. The alarm must appear in the HMI alarm view within one scan cycle of the configured acquisition time.

TIA Portal V11 caveat: in V11 (without SP2 cumulative update 5) a known issue causes the alarm subsystem to enter a degraded state after a hot restart of the HMI runtime. The temporary fix is a full project download. The permanent fix is to upgrade the TIA Portal installation to V11 SP2 + UD5 or to V12. The exact Knowledge Base entry from Siemens Industry Online Support describing this is searchable under the term "WinCC V11 alarm missing after HMI restart".

Verification

After applying any of the four solutions above, run the following verification sequence. A green pass on all four steps confirms that the alarm subsystem is fully online.

1. Status line check. Open Graphics Designer, drop an Alarm Control, and start runtime. The status line at the bottom of the control must read Ready. Strings such as No connection to data server, Initializing, or Offline mean the fix is incomplete.
2. Manual trigger test. From STEP 7 / PLCSIM, force the trigger bit of a configured alarm. Within 1–2 s the alarm row must appear in the Alarm Control with the correct timestamp, message text, and trigger point.
3. Acknowledge test. Click the Acknowledge button on the alarm row (or send the acknowledge bit from PLCSIM). The row must change from the unacknowledged color (default: red/orange) to the acknowledged color (default: white or pale green) and the Acknowledged column must populate with the time of acknowledgement.
4. Archive test (optional, if Tag Logging is in use). Stop and restart the WinCC Runtime. Trigger the alarm a second time. The historical alarm view (or the SQL alarm archive export) must contain both occurrences. If only the second one is present, the archive is not being flushed on shutdown; check the Alarm Logging → Backup settings.

Common Pitfalls and Field Notes

• Server package generated on a different computer. In distributed WinCC projects the server package is bound to the original computer name. If you copy the project to a test PC, regenerate the package on that PC, otherwise the Alarm Logging service rejects the foreign package.
• PLCSIM closed between sessions. PLCSIM does not persist state across WinCC Runtime restarts. If PLCSIM is not running when WinCC starts, the channel goes to Disconnected and the alarm trigger conditions are not evaluated. Start PLCSIM before WinCC Runtime.
• Firewall on Windows 7/10/11. The default Windows firewall blocks the internal WinCC DCOM and ALG ports. The WinCC installer usually adds firewall rules, but a manual hardening pass can remove them. Symptom: tag communication works (TCP) but alarm server does not start. Add an inbound rule for CCAlgServer.exe and the WinCC OPC ports.
• Antivirus quarantine of CCAlgServer.exe. Some aggressive endpoint protection tools (CrowdStrike, Sentinel One, Defender with Controlled Folder Access enabled) quarantine the alarm server binary on first launch. The fix is to add the WinCC install directory and the project directory to the AV exclusion list.
• Project language mismatch. WinCC is bilingual internally (operating language vs. configuration language). A mismatch between the alarm message text in language 1 and the placeholder tag in language 2 can cause the message to be rejected silently. Check Computer → Language Settings.
• Time jump after project reactivation. If the WinCC project is reactivated by double-clicking the .mcp file instead of being opened in WinCC Explorer, the runtime will be missing the server package the explorer would normally auto-load. Always use the WinCC Explorer to reactivate a project after a server-package change.

Troubleshooting Matrix

Symptom	Most Likely Cause	First Action
"No connection to data server" in Alarm Control, tags green	Server package not generated or stale	Server → Load Server Package
Alarm Control: "Initializing" for >30 s, then offline	ALM license missing / expired	Open Automation License Manager and transfer license
Alarm Control: "No connection to server" (different wording)	Channel unit disconnected, not alarm subsystem	Check Tag Management status, not Server
Tag list empty after PLCSIM restart	PLCSIM was started after WinCC Runtime	Stop WinCC, start PLCSIM, start WinCC
Alarms appear once, then stop after project edit	Server package not regenerated after edit	Server → Load Server Package
Status reads "Ready" but alarm rows are blank	Message text references an undefined tag	Alarm Logging → Message → verify all {TagName} placeholders
TIA Portal V11 only: alarms missing after HMI restart	Known V11 issue (HMI restart bug)	Upgrade to V11 SP2 UD5 or to V12
Service "SIMATIC WinCC AlarmLogging" fails with error 1053	Corrupted alarm archive database	Rename <Project>\<Computer>\ALG, regenerate package

Key Files and Paths

Item	Default Path	Purpose
Server package (V6)	<Project>\<Computer>\Packages\*.pck	Binary message/tag descriptor
Server package (V7)	<Project>\<Computer>\<Project>.srtp	Binary message/tag descriptor
Alarm Logging database	<Project>\<Computer>\ALG\	CCAlg message store
WinCC startup list	<Project>\<Computer>\<Computer>.ini	Defines which services auto-start
WinCC runtime logs	<Project>\<Computer>\Diagnostics\	Detailed start-up error reasons
Automation License Manager view	Start → SIMATIC → Automation License Manager	License state inspection

Quick Command Reference

# Start the alarm service from a Windows command line
net start "SIMATIC WinCC AlarmLogging"

# Stop the alarm service
net stop "SIMATIC WinCC AlarmLogging"

# Re-register the alarm service if it has been removed
<WinCC_Install_Path>\bin\CCAlgServer.exe /regserver

# Open the WinCC diagnosis window for live error inspection
Start → SIMATIC → WinCC → WinCC Diagnosis

References (Siemens Industry Online Support)

• Siemens Industry Online Support – entry portal for SIMATIC WinCC and STEP 7 manuals, KB articles, and firmware
• SIMATIC WinCC V7.4 SP1 – Working with WinCC Explorer (manual)
• SIMATIC WinCC V7.4 SP1 – Alarm Logging (configuration manual)
• SIMATIC WinCC V7.4 SP1 – Communication (S7 channel and PLCSIM)
• SIMATIC WinCC V7.4 SP1 – Server Packages and Distributed Systems
• SIMATIC S7-PLCSIM V5.4 SP8 – Installation and Use
• Automation License Manager V6.0 – User Guide
• WinCC V7 – "Alarm Control shows No Connection to Data Server" knowledge base entry