---
title: "Daikin Altherma 3 (Alternative Template)"
description: "Daikin Altherma 3 via DCOM-LT/MB Modbus RTU: 14 devices for heat pump mode, weather curve, DHW setpoint, temperatures and status. Alternative template."
url: "https://taphome.com/en/compatibility/daikin-altherma-3-alternatives/"
language: en
lastmod: 2026-11-15
generator: hugo
ai:
  topics: ["modbus-rtu","heat-pump","rs485","dip-switch","p1p2-bus","weather-dependent","dhw"]
  questions: ["How to integrate Daikin Altherma 3 with TapHome via Modbus?","What does the alternative Daikin Altherma 3 TapHome template monitor and control?","How to connect the DCOM-LT/MB gateway to TapHome via RS-485?","How to configure the DCOM-LT/MB DIP switch for the Modbus address?","What is the difference between the Daikin Altherma 3 TapHome templates?","Why do Daikin Altherma 3 registers return 32765 in TapHome?","How to set the weather-dependent setpoint mode of Daikin Altherma 3 in TapHome?"]
---

# Daikin Altherma 3 (Alternative Template)

Communication: Modbus RTU

## Integration guide

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](https://taphome.com/en/compatibility/daikin-altherma-3/) (20 devices). For a wider scope, see that template or the advanced [Daikin Altherma 3 DCOM-RW](https://taphome.com/en/compatibility/daikin-altherma-3-dcom-rw/) template with service attributes and service actions.

> [!NOTE]
> 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

![DCOM-LT/MB gateway component layout showing terminals, LEDs and DIP switches](https://taphome.com/images/compatibility/daikin-altherma-3-alternatives/wiring-diagram-p001_hu_f5d69e28ad5222cd.jpg)

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)

> [!WARNING]
> 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.

> [!NOTE]
> **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).

> [!WARNING]
> **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

![DCOM-LT/MB wiring detail and DIP switch address reference table](https://taphome.com/images/compatibility/daikin-altherma-3-alternatives/wiring-diagram-p003_hu_7dc5fc3bf6d653b1.jpg)

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 |

> [!TIP]
> 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).

> [!NOTE]
> 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 |

> [!TIP]
> 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](https://taphome.com/en/compatibility/daikin-altherma-3/) and [Daikin Altherma 3 DCOM-RW](https://taphome.com/en/compatibility/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)

1. Check P1P2 cable connections between DCOM-LT/MB and the Altherma indoor unit
2. Verify the Altherma unit is powered on and operational
3. Allow up to 8 minutes for initial synchronization — if the Status LED remains yellow for more than 10 minutes, the DCOM will retry automatically
4. If Status LED flashes red (timeout), verify P1P2 wiring and restart the DCOM

### RS-485 LED red (communication errors)

1. Check RS-485 wiring: + (terminal 3) to A+/D+, - (terminal 4) to B-/D-, C (terminal 5) to common
2. Verify the Modbus slave address on DIP switches SW1.3 and SW1.4 matches TapHome configuration
3. Confirm communication parameters: 9600 baud, 8 data bits, no parity, 1 stop bit
4. 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.

## Available devices 14

These devices appear in TapHome after import.

Daikin Altherma 3 Module

Dezinfekcia Variable

Read

```taphome
MODBUSR(A, 33, int16)
```

Equitermika - Krivka Thermostat

Read temperature

```taphome
ROUND(MODBUSR(H, 1, Int16))
```

Read desired temperature

```taphome
ROUND(MODBUSR(H, 1, Int16))
```

Write desired temperature

```taphome
MODBUSW(H, 1, Int16, ROUND(Se))
```

Equitermika - Posun Thermostat

Read temperature

```taphome
MODBUSR(H, 54, Int16)
```

Read desired temperature

```taphome
MODBUSR(H, 54, Int16)
```

Write desired temperature

```taphome
MODBUSW(H, 54, Int16, Se)
```

Chod Kompresor Variable

Read

```taphome
MODBUSR(A, 31, int16)
```

Chyba Variable

Read

```taphome
MODBUSR(A, 21, Int16)
```

Mod Tepeplneho Cerpadla Multi-value Switch

Values / States: AUTO · Ohrev · Chladenie

Read switch state

```taphome
MODBUSR(H, 3, Int16)
```

Write switch state

```taphome
MODBUSW(H, 3, Int16, Mu)
```

Obehove Cerpadlo Variable

Read

```taphome
MODBUSR(A, 30, Uint16)
```

Poloha Ventilu Variable

Read

```taphome
MODBUSR(A, 37, Uint16)
```

Prietok (l/m) Variable

Read

```taphome
MODBUSR(A, 49, Int16) / 100
```

Teplota TUV Thermostat

Read temperature

```taphome
MODBUSR(H, 10, Int16)
```

Read desired temperature

```taphome
MODBUSR(H, 10, Int16)
```

Write desired temperature

```taphome
MODBUSW(H, 10, Int16, Se)
```

Teplota TUV - aktualna Temperature Sensor

Read temperature

```taphome
MODBUSR(A, 43, Int16) / 100
```

${adddevice\_multivalueswitch} Multi-value Switch

Values / States: Pevne kurenie · Kurenie - Pocasie · Pevne + Plan · Pocasie + Plan

Read switch state

```taphome
MODBUSR(H, 53, Int16)
```

Write switch state

```taphome
MODBUSW(H, 53, Int16, Mu)
```

Vonkajsia Teplota - TC Temperature Sensor

Read temperature

```taphome
MODBUSR(A, 44, Int16) / 100
```

Zapnut kurenie Switch

Values / States: ON · OFF

Read switch state

```taphome
MODBUSR(H, 4, Int16)
```

Write switch state

```taphome
MODBUSW(H, 4, Int16, St)
```

**Connection:** Modbus RTU • 9600 baud• 8N1 • Slave ID: $\[SlaveId]

## Import parameters

Enter these values when you import the XML.

| Asked in the app | Default       |
|------------------|---------------|
| Slave Id         | `1`           |
| IP address       | `192.168.1.0` |

## Related Documentation

- [Modbus Integration](https://taphome.com/en/compatibility/modbus-guide/)
- [Modbus](https://taphome.com/en/docs/integration/modbus/)
- [Simple configuration using templates](https://taphome.com/en/docs/integration/modbus/templates/)
- [Modbus scripts and prefetch](https://taphome.com/en/docs/script/modbus-scripts/)
- [Modbus functions](https://taphome.com/en/docs/script/modbus/)
- [Modbus data types](https://taphome.com/en/docs/script/modbus-data-types/)