Daikin
The Daikin Altherma 3 is an air-to-water heat pump series covering Altherma 3 R, Altherma 3 H MT and Altherma 3 H HT models. TapHome connects to the heat pump through the DCOM-LT/MB Modbus RTU gateway, which interfaces with the Altherma via the P1P2 bus and exposes registers over RS-485.
This is an alternative, simpler TapHome template with 14 devices: space heating mode and weather-dependent setpoints, DHW setpoint, outside and DHW temperature, flow rate and basic status values. It uses the same gateway, communication parameters and register map as the main template Daikin Altherma 3 (20 devices). For a wider scope, see that template or the advanced Daikin Altherma 3 DCOM-RW template with service attributes and service actions.
Device names and the value labels of the multi-value switches in this template are in Slovak. They can be renamed after import.
Hardware connection
DCOM-LT/MB gateway overview
The DCOM-LT/MB gateway (model S34-001) mounts on a DIN rail and has the following connections:
- Terminals 1–2 (A) — Power supply: 15–24 VDC regulated, minimum 100 mA
- Terminals 3–5 (B) — RS-485: + (terminal 3), - (terminal 4), C/common (terminal 5)
- Terminals 10–11 (E) — P1P2 bus connection to Altherma indoor unit
- SW1 (J) — 8-position DIP switch for Modbus address and operating mode
- LEDs (P, Q, R) — Status, ACNET (P1P2), RS485 indicators
RS-485 wiring
Connect using a 3-wire RS-485 connection between DCOM-LT/MB and TapHome:
- Terminal 3 (+) → A+/D+ on TapHome RS-485
- Terminal 4 (-) → B-/D- on TapHome RS-485
- Terminal 5 (C) → GND/Common on TapHome
Cable specification:
- Type: screened twisted pair (Belden 8761 or equivalent)
- Minimum cross-section: 0.33 mm²
- Resistance: ≤ 60 Ω/km
- Max bus length: 1000 m
- Max devices on bus: 32 (including Modbus master)
The common wire (terminal 5/C) must be connected between DCOM-LT/MB and TapHome. Without a proper common connection, communication errors will occur. Shield should be earthed at one location only.
Termination is not required at 9600 baud for network lengths up to 1000 m. The DCOM-LT/MB has internal failsafe biasing, so no external bias resistors are needed. If termination is used, a failsafe biasing circuit must be added as well.
P1P2 connection
Connect the P1P2 terminals (10, 11) to a compatible Altherma LT Master Remote Controller (e.g., MM4 or equivalent).
Altherma 2 compatibility: The DCOM-LT/MB can only be used with Altherma 2 via the Remcon/LT LAN adaptor. Do NOT connect DCOM directly to Altherma 2 (EKRUCBL / EKRUEHBL) units.
Configuration
DIP switch addressing
The 8-position DIP switch SW1 configures the Modbus slave address and operating mode:
| Switch | Function |
|---|---|
| SW1.1 + SW1.2 | Smart Grid / operating mode select |
| SW1.3 + SW1.4 | Modbus slave address (1–4) |
| SW1.5 | Smart Grid function (with SW1.1, SW1.2) |
| SW1.6–SW1.8 | Reserved |
Modbus address selection (SW1.3 and SW1.4):
| SW1.3 | SW1.4 | Address |
|---|---|---|
| OFF | OFF | 1 (default) |
| OFF | ON | 2 |
| ON | OFF | 3 |
| ON | ON | 4 |
The template uses Slave ID 1 by default, matching the factory DIP switch setting.
Communication parameters
| Parameter | Value |
|---|---|
| Protocol | Modbus RTU |
| Baud rate | 9600 |
| Data bits | 8 |
| Parity | None |
| Stop bits | 1 |
In TapHome, the template is imported on the RS-485 bus the gateway is wired to, with the Slave ID set to the address selected on SW1.3 and SW1.4.
Synchronization
After power-up, the DCOM-LT/MB synchronizes with the Altherma Master unit. This process can take up to 8 minutes. During synchronization, register reads return the special value 32765 (“Wait for value”).
Special return values:
| Value | Meaning |
|---|---|
| 32765 | Waiting for value — synchronization in progress |
| 32766 | Register unavailable in current configuration |
| 32767 | Register not supported by connected unit |
After initial power-up or restart, allow up to 8 minutes for DCOM to fully synchronize before troubleshooting missing register values. The Status LED changes from yellow (synchronizing) to solid green when ready.
Device capabilities
The template creates one Modbus module with 14 devices. Setpoints and switches are polled every 2.5 s, status values and sensors every 15 s.
Temperature and flow monitoring
The temperature sensors use the temp16 format (signed 16-bit value divided by 100 for °C). The template handles this conversion automatically.
- Outside Air Temperature (A:44) — outdoor ambient temperature
- DHW Temperature (A:43) — domestic hot water tank temperature, a separate temperature sensor
- Flow Rate (A:49) — water flow rate in l/min (register value divided by 100)
Space heating control
- Space Heating On/Off (H:4) — switches space heating on or off and shows its current state
- Heat Pump Mode (H:3) — operation mode: Auto, Heating, or Cooling
- Multi-Value Switch (H:53) — setpoint mode: Fixed, Weather Dependent, Fixed + Scheduled, or Weather Dependent + Scheduled. The device is imported under the generic name “Multi-Value Switch”; renaming it (for example to “Setpoint Mode”) after import is recommended
- Weather Curve Setpoint (H:1) — leaving water main heating setpoint, range 25–55°C
- Weather Curve Offset (H:54) — weather dependent setpoint offset, range -10 to +10°C
DHW (Domestic Hot Water) control
- DHW Setpoint (H:10) — DHW reheat setpoint temperature, range 30–60°C
The setpoint thermostats (H:1, H:54, H:10) read the setpoint register for both the desired and the current value, so their current value shows the setpoint, not a measured temperature. The measured DHW temperature is the separate DHW Temperature sensor (A:43).
The usable setpoint range is determined by the minimum and maximum setpoints configured in the Altherma field settings. If a written setpoint is outside the configured range, the DCOM sets it to the nearest valid minimum or maximum.
System status monitoring
These devices are Modbus variables that show the raw register value:
| Device | Register | Values |
|---|---|---|
| Unit Error | A:21 | 0 = No Error, 1 = Fault, 2 = Warning |
| Compressor Run | A:31 | 0 = OFF, 1 = ON |
| Circulation Pump | A:30 | 0 = OFF, 1 = ON |
| Disinfection Operation | A:33 | 0 = OFF, 1 = ON |
| 3-Way Valve Position | A:37 | 0 = Space Heating, 1 = DHW |
The other DCOM-LT/MB registers, such as leaving and return water temperatures, refrigerant temperature, defrost status, quiet mode, DHW reheat and booster mode, are covered by the Daikin Altherma 3 and Daikin Altherma 3 DCOM-RW templates.
LED status indicators
The DCOM-LT/MB has three LED indicators:
| LED | Normal | Error |
|---|---|---|
| Status | Solid green — synchronized, no fault | Solid red — unit fault; slow red blink — timeout |
| ACNET | Green flash — normal P1P2 communication | Red flash/solid — P1P2 errors |
| RS485 | Green flash — normal Modbus communication | Red flash/solid — RS-485 errors |
At power-up, all LEDs change from red to green, then the Status LED begins flashing yellow while waiting for Altherma Master synchronization.
Troubleshooting
Status LED yellow (waiting for Master)
- Check P1P2 cable connections between DCOM-LT/MB and the Altherma indoor unit
- Verify the Altherma unit is powered on and operational
- Allow up to 8 minutes for initial synchronization — if the Status LED remains yellow for more than 10 minutes, the DCOM will retry automatically
- If Status LED flashes red (timeout), verify P1P2 wiring and restart the DCOM
RS-485 LED red (communication errors)
- Check RS-485 wiring: + (terminal 3) to A+/D+, - (terminal 4) to B-/D-, C (terminal 5) to common
- Verify the Modbus slave address on DIP switches SW1.3 and SW1.4 matches TapHome configuration
- Confirm communication parameters: 9600 baud, 8 data bits, no parity, 1 stop bit
- For long cable runs, verify cable impedance and consider adding termination
Registers returning 32765
This indicates the DCOM is still synchronizing with the Altherma Master. Wait up to 8 minutes after power-up. If the value persists, check the Status LED — it should be solid green when synchronization is complete.
Unit Error shows 1 (Fault)
While the DCOM is waiting for or synchronizing with the Altherma Master, Unit Error (A:21) reads 0 (No Error). If the DCOM times out waiting for the Master, Unit Error is set to 1 (Fault) and the Status LED flashes red — check the P1P2 wiring as described above. Otherwise, the fault is reported by the Altherma unit itself; refer to the installation and operation manual of the Altherma system for the meaning of fault codes.
