The AUX ACHP-H is an air-to-water monobloc heat pump (R290/R32) for space heating, cooling and domestic hot water. The manufacturer documents used for this page cover the R290 monobloc range ACHP-H04 to ACHP-H16. TapHome talks to the heat pump over Modbus RTU on an RS-485 line, in one of two ways:
- Directly on the XK08 wired controller — the controller has its own RS-485 port for a BMS (building management system) and its own Modbus page in the Options menu. No extra hardware is needed.
- Through the AUX Modbus Gateway — a separate RS-485 to RS-485 gateway between the heat pump and TapHome, addressed with DIP switches.
The template switches the heat pump on and off, selects the operating mode, sets the water and hot water setpoints, controls ECO, weather compensation and silent mode, forces the tank electric heater on or off or leaves it to the heat pump, shows when the pipe backup heater and the tank electric heater run, reads temperatures, water flow, electrical power, heating capacity, COP and today’s energy, and turns outdoor and indoor unit fault codes into TapHome notifications with the code as shown on the display.
Communication parameters
Both connection paths use the same serial settings. They match the template defaults:
| Parameter | Value |
|---|---|
| Protocol | Modbus RTU |
| Baud rate | 9600 bps |
| Data bits | 8 |
| Parity | Even |
| Stop bits | 1 |
| Slave ID | 1–255 (template default 1) |
| Supported function codes | 03 read holding register, 06 write single register, 16 write multiple registers |
The manufacturer states that the heat pump supports only function codes 03, 06 and 16. Coil functions, which the gateway itself offers for other AUX products, do not apply to the heat pump.
Option A — direct connection to the XK08 wired controller
Wiring
The XK08 wired controller is mounted on the wall and connected to the main control board of the hydraulic module. On the terminal block on the back of the controller, the manufacturer marks one pair of terminals as “Signal to BMS/Central controller” (marker ① in the manufacturer’s figure, terminals labelled B and A). The template description refers to this pair as A2/B2. The other terminals (B, A, 24V, GND and the plug-in socket) carry the communication with the hydraulic module and must stay as they are.
- Switch off the power of the indoor unit, as the manufacturer requires before opening the controller.
- Open the back cover: pry the bottom groove gently with a flathead screwdriver. Too much force damages the circuit board.
- Connect a 2-core shielded cable from the BMS terminal pair to the RS-485 bus of TapHome: A to A, B to B.
- Route the communication cable separately from power cables.
- Refit the controller body: push the upper part into the clip first, then the lower part.
The AUX manuals used here contain a figure of the XK08 terminal block but no wiring diagram from those terminals to a BMS. Check the labels on the controller itself before connecting, and do not touch the B, A, 24V and GND terminals of the hydraulic module link.
Enabling Modbus on the XK08
- On the controller, open the Options page.
- Select Modbus and press the confirm button to enter the Modbus page.
- Set Slave ID with the arrow buttons. Write the value down — TapHome needs it.
- Check Baud rate = 9600Bd and Parity check = Even.
Option B — connection through the AUX Modbus Gateway
Gateway ports and power
The gateway has two RS-485 ports and three indicator lamps:
| Port or lamp | Purpose |
|---|---|
| RS485-1 | To the heat pump’s RS-485 port (terminals A, B). Polarity does not matter on this port. |
| RS485-2 | To the BMS, here TapHome. |
| DC 12V | Power supply — the installer provides an adapter with 12 V DC output and at least 300 mA. |
| POWER lamp | Lights steadily when the gateway is powered. |
| 485-1 lamp | Flickers when the gateway communicates normally with the heat pump. |
| 485-2 lamp | Flickers when the gateway communicates normally with TapHome. |
The gateway belongs in an electrical cabinet, front facing outward and terminals facing down, fixed horizontally with two screws.
The AUX documents used here do not show where the RS-485 port (A, B) for the gateway is located on the ACHP-H unit. Ask the AUX distributor for the exact terminal before wiring.
Wiring
- Connect the gateway’s RS485-1 to the heat pump’s RS-485 port (A, B).
- Connect the gateway’s RS485-2 to the RS-485 bus of TapHome.
- With several gateways, run the RS485-2 line from the first gateway to the next one in a daisy chain.
- Set the DIP switches (below) before powering up.
Cable requirements from the manufacturer, for both lines:
- Shielded PVC-sheathed twisted-pair copper cable (type RVVSP), at least 2 × 0.75 mm².
- At most 800 m per line. On the heat pump side, the total length includes the communication wiring between the indoor and outdoor unit.
- Above 800 m in total, more than 30 gateways, or with an unstable signal, add a repeater.
Gateways must be connected in a daisy chain (“hand in hand”). Star and Y-shaped connections are forbidden. The power cable and the communication cables must be routed separately, otherwise the gateway may be damaged.
DIP switch SW1 — function and line termination
For a heat pump, set SW1-2 = ON, SW1-3 = OFF, SW1-4 = OFF (“Modbus (Heat pump)”).
SW1-1 connects the gateway’s 120 Ω matching resistor, which belongs to the RS485-2 side. When the communication line is longer than 300 m, the line must be terminated at both ends: set SW1-1 to ON on the gateway at the end of the line and add a 120 Ω resistor at the other end.
DIP switch SW2 — Modbus address
SW2 is an 8-bit binary switch that sets the gateway’s Modbus address, 1–255. All switches off (address 0) is not valid. SW2-1 is the highest bit (128) and SW2-8 the lowest (1). Example from the manual: address 26 = SW2-4, SW2-5 and SW2-7 ON, all others OFF. Every gateway on the same line needs a different address, otherwise communication fails.
DIP switch settings take effect only after the gateway’s power is switched off and on again.
The manual’s heat pump register table for the gateway ends at register 73. Water flow, today’s energy, defrost, heating capacity, electrical power, COP and the related service attributes (registers 86–99) are listed only in the XK08 controller manual. Through the gateway these values may not be available. The same applies to the tank electric heater control (register 411) and the tank heater TBH attribute (register 268).
Adding the heat pump in TapHome
Import the template on the Modbus RTU interface the heat pump is wired to, set the interface to 9600 bps, 8 data bits, even parity and 1 stop bit, and enter the Slave ID (XK08: Options → Modbus; gateway: DIP switch SW2).
Device capabilities
All values are holding registers. Temperatures and setpoints are transferred in 0.1 °C.
Heat pump control
| Device | What it does | Register |
|---|---|---|
| Heat pump on/off | Switches the unit on or off | 0 |
| Operating mode | Auto, Cooling or Heating | 1 |
| Water temperature setpoint | Thermostat: target water temperature (register 2), current temperature from the plate heat exchanger water outlet (register 65) | 2, 65 |
| ECO mode | Off or ECO 1–8 | 5 |
| Weather compensation | Off or automatic water temperature curve Auto 1–9 | 6 |
| Silent mode | Off, Silent 1 or Silent 2 | 13 |
The manufacturer’s tables give 5–25 °C for the cooling setpoint. For heating, the gateway manual gives 25–65 °C and the XK08 manual 25–80 °C. Keep the setpoint within the range of the unit and connection path in use.
Domestic hot water
| Device | What it does | Register |
|---|---|---|
| Hot water on/off | Switches hot water heating on or off | 3 |
| Hot water setpoint | Target tank temperature in °C (gateway manual 30–60 °C, XK08 manual 30–75 °C) | 4 |
| Fast hot water | Fast DHW heating on or off | 8 |
Backup heaters
| Device | What it does | Register |
|---|---|---|
| Pipe backup heater | Shows On while the pipe backup heater runs (read only) | 61 |
| Tank electric heater | Shows On while the electric heater in the hot water tank runs; the manufacturer calls it the tank backup heater (read only) | 62 |
| Tank electric heater control | Auto, Forced off or Forced on for the tank electric heater | 411 |
Tank electric heater control writes 0 for Forced off and 1 for Forced on. Auto writes 32768 (0x8000), which cancels the forced control and leaves the heater to the heat pump’s own control; any register value other than 0 or 1 is shown as Auto. The manufacturer lists register 411 only in the XK08 controller’s register table.
Temperatures
| Device | Register |
|---|---|
| Suction temperature | 50 |
| Discharge temperature | 51 |
| Exchanger temperature | 52 |
| Outdoor temperature | 53 |
| Water inlet temperature (plate heat exchanger) | 64 |
| Hot water tank temperature | 66 |
| Floor heating outlet temperature | 67 |
| Floor heating inlet temperature | 68 |
| Room temperature (zone 1) | 69 |
Flow, power and efficiency
These registers come from the XK08 controller’s register table.
| Device | Unit | Register |
|---|---|---|
| Water flow | m³/h | 86 |
| Electrical power | kW | 93 |
| Heating capacity | kW | 91 |
| COP | — | 95 |
| Energy consumed today | kWh | 87 |
Notifications
The module reads the status registers and raises:
- Error “Outdoor unit fault …” when register 70 is not 0, and “Indoor unit fault …” when register 71 is not 0, followed by the fault code as on the display, for example “Outdoor unit fault A1”.
- Information “Defrosting” while the unit defrosts (register 88).
Whether the pipe backup heater or the tank electric heater runs is shown by their own devices (see Backup heaters).
Service attributes and actions
In the module’s service view, the template shows outdoor unit capacity and operating mode, compressor frequency, target frequency, current, pressure and run time, fan speed, expansion valve position, DC bus voltage, inverter input current and module temperature, average power and COP over the last hour, the software versions of the outdoor and indoor unit (decoded from the manufacturer’s BCD code, for example V1.0) and of the wired controller, and the state of the advanced settings (DHW mode, disinfection, DHW priority, cooling and heating mode enabled, water or room temperature control, double zone, tank heater TBH, indoor backup heater).
Service actions:
- Run DHW pump and Start disinfection — one-off commands; the manufacturer notes that the water module ends them automatically.
- Set DHW mode, Set disinfection enabled, Set DHW priority, Set cooling mode enabled, Set heating mode enabled, Set water temperature control, Set room temperature control, Set double zone, Set indoor backup heater — On/Off for the advanced parameters in registers 200–241.
The XK08 manual limits the number of control commands to an indoor unit to 1 million. The template writes a register only when its value changes; avoid smart rules that rewrite setpoints or modes in short cycles.
Troubleshooting
No response from the heat pump
- Check that the Slave ID in TapHome equals the value on the XK08 Modbus page or on gateway switch SW2.
- Check the serial settings on both sides: 9600 bps, 8 data bits, even parity, 1 stop bit.
- XK08: check that the cable is on the BMS terminal pair, not on the hydraulic module terminals, and that A and B are not swapped.
- Gateway: check SW1 (SW1-2 ON, SW1-3 OFF, SW1-4 OFF) and switch the gateway’s power off and on after any DIP switch change.
- Gateway: two gateways with the same address on one line make communication fail.
Gateway indicator lamps
| Symptom | Possible causes (manufacturer) |
|---|---|
| POWER lamp off | No 12 V supply, reversed 12 V polarity, faulty main supply or gateway |
| 485-1 lamp does not flicker | Wrong SW1 setting, heat pump without power, wrong port or poor connection on RS485-1 |
| 485-2 lamp does not flicker | Wrong SW1 or SW2 setting, TapHome without power, wrong port or poor connection on RS485-2 |
Communication errors right after start (gateway)
RS485-2 identifies the line polarity by itself. It needs continuous traffic — more than 300 bytes or 5 frames — before it switches to the correct polarity, so the first requests after power-up may fail. If errors persist, check the cable length and the termination (SW1-1) for lines over 300 m.
Reading the fault code
TapHome shows the fault code in hexadecimal, as on the heat pump’s display, for example “Outdoor unit fault A1” for fault A1. The template shows the digits as the unit sends them: the digit B in TapHome stands for the display character H and D for J. Look the code up in the fault table of the heat pump’s service manual.
Water flow, power or COP stay at 0 through the gateway
These values (registers 86–99) are documented only for the XK08 controller. If they do not update through the AUX Modbus Gateway, connect TapHome directly to the XK08 instead.
