Tecalor THZ (SG Ready)
The Tecalor THZ (SG Ready) is a residential heat pump controller used in heating and domestic hot water applications, accessed via Modbus TCP through the Tecalor Internet Service Gateway (ISG). This template reads the current SG Ready operating state and a temperature value, and writes the two SG Ready control registers that enable the function and set the demand input. Together these registers let your ModbusCloud portal shift heat pump load toward times of PV surplus, turning grid-interactive control into logged, auditable data.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 4, read and write
- Brand
- Tecalor
- Compatible models
- LWA/LWZ (SG Ready) · THZ (SG Ready)
- Last updated
Registers (4)
2 read, 2 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| getmode | Read | ||||
| setmode_a | Write | ||||
| setmode_b | Write | ||||
| temp | °C | Read |
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If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Monitor the current SG Ready operating state to verify the heat pump responds correctly to PV surplus signals.
- Track temperature readings over time to detect sensor faults or unexpected thermal drift in the system.
- Alert on unexpected SG Ready state transitions that may indicate a control conflict between the ISG and another automation system.
- Compare logged SG Ready activation events against energy-meter data to verify self-consumption improvements.
- Verify that both SG Ready write registers remain consistent after a gateway restart or ISG firmware update.
Installation
Enable Modbus TCP on the Tecalor ISG by navigating to the communication or ISG section of the device web interface, then confirm that the ISG firmware is at a version that supports simultaneous Modbus and other ISG functions.
Connect the ModbusCloud Gateway to the same LAN segment as the Tecalor ISG, and note the ISG IP address either from your router's DHCP table or from the ISG web interface.
In the ModbusCloud portal, add a new device, select Modbus TCP, enter the ISG IP address and port 502, set the unit ID to 1, and import the Tecalor THZ (SG Ready) template.
Spot-check the connection by reading register 5000 (getmode) in the portal's live register view and confirm it returns a value of 1 through 4, matching the expected SG Ready state on the ISG status screen.
Things to watch for
Register 5000 always returns 32768. What does that mean?
A value of 32768 (0x8000) is the Tecalor ISG sentinel for an unavailable object. This typically means the ISG firmware version does not expose the SG Ready status register for your connected heat pump model, or the Modbus feature is not fully enabled. Check that SG Ready is activated in the ISG menu and that the ISG firmware is current.
The gateway connects but writing setmode_a and setmode_b has no effect.
The ISG uses 1-based addressing, so some Modbus clients must apply an offset of 1. Confirm that your portal's Modbus TCP client targets port 502 and unit ID 1. Also verify that the SG Ready function is enabled in the ISG web interface before writing to the control registers, as writes are silently ignored when SG Ready is disabled at the device level.
What are the risks of writing to the SG Ready setpoint registers?
Writing incorrect values to setmode_a or setmode_b can place the heat pump into an unintended operating mode, potentially overriding comfort setpoints or triggering the forced-on state (mode 4) outside of intended hours. Always test write commands manually first, ensure you can revert to mode 2 (normal operation), and consult the Tecalor Modbus documentation before automating writes in production.
The ISG becomes very slow or stops responding after polling starts.
The Tecalor ISG web interface and Modbus TCP share processing resources. Polling at intervals shorter than 30 seconds can overload the ISG, causing slow responses or dropped connections. Set your ModbusCloud Gateway poll interval to at least 30 seconds. Also confirm that no other Modbus clients (for example, ioBroker or Home Assistant) are polling simultaneously.
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