A Walchem Modbus Unlock Key is a vendor‑specific security/licensing code used on many Walchem controllers (W600, W900 series, etc.) to enable Modbus communications access—especially write access—that is otherwise locked out by default.
This is not part of the Modbus protocol itself. It’s a Walchem security feature.
It is:
Controller‑specific
Required for control changes
Provided by Walchem or their distributors
Not part of the Modbus protocol itself
This prevents accidental or unauthorized control changes.
Note: You can verify if Modbus/BACnet is available in an I6 or I9 by going to the “config” menu and looking for the “remote communications” option. It only appears if a Key is active. It also must be “enabled” via setting change by the operator even after the key is installed.
To obtain a Modbus Key:
To obtain a Modbus Key:
Customer to provide:
Model number (I9 / Model WIN9AOOOPNNNNNNN-NNNNNN)
Serial number (SER # 23070700171)
Firmware version (if available)
APS will order the key from Walchem (See Paul Peacock or tom Tinney for assistance here)
APS forwards the key via email to Customer
Customer loads the key via USB drive into the controller using the Software Upgrade feature on the controller.
Where to Enter the Unlock key
Where to Enter the Unlock key
For W100 / W600 / W900 series controllers, the unlock key is entered from the local keypad.
Typical Menu Path
(wording may vary slightly by firmware)
Menu → Setup → Communications → Modbus → Security (or Advanced) → Unlock Modbus
You’ll be prompted to enter the numeric unlock key provided by Walchem.
✅ Once accepted:
Modbus writes are enabled
Reads continue to work as normal
✅ Touchscreen Models (W900 / Newer Units)
On touchscreen-equipped controllers:
Main Menu → Configuration → Communications → Modbus → Security → Modbus Unlock Key
Enter the key and confirm.
✅ Web Interface (If Ethernet Is Enabled)
On some models (typically W900 with firmware supporting web access):
Browse to the controller’s IP address
Log in (appropriate user level required)
Navigate to:
Settings → Communications → Modbus → Security
Enter the Modbus Unlock Key
⚠️ Note:
Many Walchem models do not allow Modbus unlock via the web UI for safety reasons—front panel entry may still be required.
What Happens After Entry?
What Happens After Entry?
Depending on model and configuration:
✅ Modbus write registers become writable
🔁 Unlock may:
Reset on power cycle or
Auto‑expire after a timeout or
Stay enabled until manually disabled
This behavior is model‑ and firmware‑specific.
If You Don’t See the Unlock Menu
Possible reasons:
Modbus not enabled yet
User access level too low
Firmware version doesn’t support Modbus writes
Controller model does not require an unlock key (some older units)
For the geek in you -
on/off activations and some functional parameters can be written to both controllers, but only the I9 can take a Modbus numeric value in (by using the Virtual inputs functions with a limit of 12 total) and treat it as a true variable input for control or monitoring purposes (Like a sensor, water meter, etc.)