The Sistema-Home 4..18(T) is a dual-circuit heat pump communicating over Modbus RTU (RS-485). The TapHome template provides operating mode control with heating, cooling, and DHW modes, setpoint adjustment for heating and cooling circuits, DHW temperature setpoint, and comprehensive monitoring of water temperatures, refrigerant pressures, fan and pump speeds, and water flow rate. The template also reports 80+ error codes from the heat pump controller via bitfield registers.
The controller is likely based on a CAREL pCO platform (typical for Italian OEM heat pumps). The register map is proprietary and all technical information in this template comes exclusively from the XML template — no public documentation is available from the manufacturer.
Hardware connection
The Sistema-Home 4..18(T) connects to TapHome via a Modbus RTU CCU gateway using an RS-485 serial bus. The default communication parameters are 9600 baud, 8 data bits, Even parity, 1 stop bit, Slave ID 1.
Connect the RS-485 wiring between the heat pump’s Modbus port and the TapHome Modbus RTU CCU:
- A+ on the heat pump → A+/D+ on TapHome RS-485
- B- on the heat pump → B-/D- on TapHome RS-485
- GND → GND (mandatory for reliable communication)
The GND wire must be connected between the heat pump and the TapHome gateway. Without proper grounding, Modbus communication errors are likely, especially on longer cable runs.
Configuration
Remote write enable
The template automatically enables remote write access on every poll cycle by setting bit 0 of register H:7201. This means the heat pump accepts setpoint and mode changes from TapHome as soon as the template is imported — no manual configuration of this register is needed.
Communication parameters
Verify the following settings match between the heat pump and TapHome:
| Parameter | Value |
|---|---|
| Baud rate | 9600 |
| Data bits | 8 |
| Parity | Even |
| Stop bits | 1 |
| Slave ID | 1 (default) |
If the Slave ID on the heat pump differs from 1, update the Slave ID import parameter in TapHome to match.
Device capabilities
Operating mode control
The Active Mode device selects the heat pump operating mode. Available modes:
| Value | Mode | Description |
|---|---|---|
| 0 | Stand by | Heat pump idle |
| 1 | Cool | Cooling only |
| 2 | Heat | Heating only |
| 4 | Sanitary | DHW production only |
| 5 | Cool+DHW | Cooling with DHW |
| 6 | Heat+DHW | Heating with DHW |
Mode values 3, 7, 8, and 9 are defined in the template but have no meaningful names — they appear as placeholder digits and may be reserved or unused on this controller variant.
A DHW (Sanitary) Setpoint service action on the Active Mode device allows setting the domestic hot water temperature target (range 25–55 °C).
Setpoint control
Two thermostat devices control heating and cooling setpoints:
- Heat Setpoint — reads/writes the heating setpoint (H:1002). The current temperature reference is the plant mixing tank sensor (H:440).
- Cool Setpoint — reads/writes the cooling setpoint (H:1001). Uses the same plant mixing tank temperature as the current value.
Both setpoints use a ×10 conversion (e.g., a register value of 350 = 35.0 °C).
Temperature monitoring
Six temperature sensors provide thermal monitoring across the system:
- Outside Temperature — ambient outdoor temperature (H:428, polled every 30 s)
- Plant Temperature (Mixing Tank) — buffer/mixing tank temperature (H:440), also used as the current temperature reference for both thermostats
- Water Inlet Temperature — heat exchanger water inlet (H:400)
- Water Outlet Temperature — heat exchanger water outlet (H:401)
- DHW Temperature — domestic hot water tank temperature (H:405), with fault detection (reports a warning if the sensor reads “Not configured” or “Fault”)
- Compressor Discharge Temperature — compressor 1 discharge temperature (H:433), with 7 service attributes covering discharge temperatures for all compressors across both refrigerant circuits
The template device named “Compressor inhalation” actually reads register H:433, which corresponds to compressor discharge 1 per the register map. The actual compressor inhalation register (H:422) is not exposed as a primary device. The display name in TapHome reflects the corrected function (Compressor Discharge Temperature).
Refrigerant pressure monitoring
Two pressure sensors monitor the refrigerant circuits:
- High Pressure — high-side refrigerant pressure in bar (H:406), with a service attribute for circuit 2 (H:20406)
- Low Pressure — low-side refrigerant pressure in bar (H:414), with a service attribute for circuit 2 (H:20414)
Fan and pump speed
- Fan Speed — read-only fan speed as percentage (H:7000, ÷1000 conversion)
- Pump Speed — read-only circulation pump speed as percentage (H:7001, ÷1000 conversion)
Water flow rate
The Water Flow Rate sensor reads the system water flow in l/min (H:444). It includes fault detection — a warning is raised if the sensor reports “Not configured” (32766) or “Fault” (32767).
The Water Flow Rate status service attribute reads register H:405 (the DHW temperature register) instead of H:444. This appears to be a template bug — the status may not accurately reflect the water flow sensor state.
Compressor runtime monitoring
Six module-level service attributes track compressor operating hours:
- Compressor 1/2/3 Runtime — cumulative hours for circuit 1 compressors (H:305, H:307, H:309)
- Compressor 1/2/3 Runtime (Circuit 2) — cumulative hours for circuit 2 compressors (H:313, H:315, H:317)
Error monitoring
The module ReadScript monitors registers H:950 through H:956 (7 bitfield registers) and reports 80+ distinct error and warning codes. Key error categories include:
- Refrigerant circuit faults — high pressure (E001), low pressure (E002), frost (E005)
- Thermal protection — compressor (E003, E013, E023), fan (E004, E014, E024), pump (E016, E026)
- Temperature faults — high discharge temperature (E009, E019, E029), high temperature (E018), incongruent temperatures (E041)
- DHW faults — poor heat exchange (E042), accumulation tank overheating (E050), anti-legionella status (E060/E061)
- Sensor errors — probe errors for up to 11 probes across 3 I/O modules (E611–E713)
- Inverter faults — link errors, hardware faults, overcurrent, overheating, voltage faults, phase sequence errors, EEPROM errors for up to 3 inverters (E801–E973)
- I/O module faults — module 1/2 disconnected (E101, E102)
Additional capabilities
The heat pump controller also exposes a compressor inhalation temperature register (H:422) and a remote write enable flag (H:7201) that is automatically managed by the template. These can be added as standalone devices in a future template update if direct monitoring of inhalation temperature is needed.
Troubleshooting
No Modbus communication
- Verify RS-485 wiring — A+ to A+, B- to B-, GND connected
- Confirm communication parameters: 9600 baud, 8E1, Slave ID 1
- Check cable length and termination — for long runs, a 120 ohm termination resistor may be needed at the last device on the bus
- Ensure the heat pump controller’s Modbus interface is enabled (consult the on-site controller menu)
Sensors showing “Not configured” warnings
Registers returning the special value 32766 indicate a sensor that is not wired or not configured on the heat pump controller. This is expected for optional sensors (e.g., DHW probe on units without a DHW tank). The warning can be acknowledged in TapHome.
Mode changes not taking effect
- Verify the Active Mode device shows the expected mode after writing — the read register (H:200) and write register (H:7200) are separate, so there may be a brief delay
- Check that no local override or lockout is active on the heat pump controller
- The remote write enable flag (H:7201 bit 0) is set automatically by the template — if communication was interrupted, it will be re-enabled on the next poll cycle
