The Nilan CTS-602 is a controller used in Nilan’s Compact P, Compact S, VP, VPL, COMBI, VGU180 and VENTEC series ventilation and heat pump units. The TapHome template connects to the CTS-602 via Modbus TCP, providing temperature monitoring, climate control, hot water management, ventilation step control and output status monitoring.
The CTS-602 natively communicates via Modbus RTU over RS-485. A Modbus RTU-to-TCP bridge device (e.g. USR-TCP232 or Waveshare RS485 TO ETH) is required to connect to TapHome.
Hardware connection
There are two ways to access the RS-485 Modbus interface, depending on the unit model and installation preference.
8-pole plug (top of unit)
On Comfort, Compact and similar models, the Modbus wires are routed through the 8-pole connector plug on top of the unit. This plug also carries the control panel, T1 sensor and user selection connections.
| Pin | Function |
|---|---|
| 1 | GND |
| 2–3 | Control panel |
| 4–5 | User selection (dry contact) |
| 6 | A1 — RS-485 Data+ (Modbus) |
| 7 | B1 — RS-485 Data- (Modbus) |
| 8 | T1 sensor (outdoor air) |
Connect the RTU-to-TCP bridge to pin 1 (GND), pin 6 (A1) and pin 7 (B1).
CN7 connector (PCB)
On CTS-602 boards with HMI350T, the RS-485 interface is also available on the 6-pin CN7 connector (next to the USB plug) directly on the PCB:
| Pin | Function |
|---|---|
| 1 | 12 VDC output |
| 2 | COM1 — RS-485 Data+ (A) — Modbus |
| 3 | COM1 — RS-485 Data- (/B) — Modbus |
| 4 | COM2 — RS-485 Data+ (A) — User panel |
| 5 | COM2 — RS-485 Data- (/B) — User panel |
| 6 | Ground |
Connect the RTU-to-TCP bridge to pins 2 (Data+), 3 (Data-) and 6 (GND) using COM1. COM2 is reserved for the HMI user panel.
The CTS-602 has no opto-isolation on the RS-485 port. Use shielded twisted-pair cable (AWG 24/0.25 mm², impedance 100–130 Ohm). Maximum cable length is 200 m. Install 120 Ohm termination resistors at each end of the bus.
Configuration
RS-485 bridge settings
Configure the RTU-to-TCP bridge with the following parameters:
| Parameter | Value |
|---|---|
| Baud rate | 19200 |
| Data bits | 8 |
| Parity | Even |
| Stop bits | 1 |
These communication parameters are fixed on the CTS-602 and cannot be changed.
Modbus slave address
The Modbus interface is always active — there is no separate “enable Modbus” setting. Only the slave address needs to be configured.
The default slave address is 30 (configurable 1–247). To change it, navigate the SERVICE menu on the CTS-602 control panel:
| |
On the older knob-based panel, use the knob to scroll through menu items. On the HMI touchscreen panel, use the touchscreen interface. The MODBUS ADR item is near the bottom of the SERVICE menu, after PWR SAVE.
TapHome import parameters
When importing the template, TapHome prompts for:
- Slave ID — default 1 in template, change to match the CTS-602 setting (default 30)
- IP Address — the IP address of the RTU-to-TCP bridge device
Device capabilities
Temperature monitoring
The template provides 9 temperature sensors covering air temperatures, hot water tank and system performance:
- Intake Temperature (T1) — fresh air intake temperature
- Exhaust Temperature (T3) — room exhaust air temperature
- Hot Water Top Temperature (T11) and Hot Water Bottom Temperature (T12) — hot water tank temperatures (top for electric heater zone, bottom for compressor zone)
- Room Temperature — actual room temperature from the T15 user panel sensor or T10 external sensor
- Inlet Temperature Setpoint — requested inlet air temperature (T7 setpoint)
- Controlled Temperature — value of the master controlled temperature sensor
- Heat Exchanger Efficiency — passive heat exchanger efficiency percentage
- Winter Temperature Threshold — low outdoor temperature threshold for ventilation reduction (configuration value)
All temperature values use a scale factor of 100 (register value 2200 = 22.00 °C).
Operating mode control
The template exposes two on/off controls and a mode selector:
- Run Actual — reads and writes the actual on/off state (H:1000)
- Run Set — user on/off control (H:1001), the standard on/off register per official documentation
- Mode Actual — current operating mode (Off, Heat, Cool, Auto, Service)
- Mode Set — operating mode selector (Off, Heat, Cool, Service, and numbered extended modes)
- Control State — active control state display with 18 states (Off, Ventilation, Heating, Cooling, Hot water, Defrost, Legionella, Central heating, Alarm, and more)
- Time in State — seconds elapsed in the current control state
Climate control
Three thermostat devices enable temperature setpoint control:
- Temperature Setpoint — room temperature setpoint, reads current temperature from the T15 room sensor and writes the desired temperature to H:1004
- Hot Water Setpoint T11 — top tank (electric heater) temperature setpoint
- Hot Water Setpoint T12 — bottom tank (compressor) temperature setpoint
Ventilation control
- Ventilation Step — current ventilation fan step (Off, 1–4), read-only
- Inlet Fan Step and Exhaust Fan Step — actual fan speed steps (Off, 1–4)
- Ventilation Level Set — ventilation fan level selector (0–4), read/write
- Winter Ventilation Step — fan speed setting at low outdoor temperature (configuration value)
Filter monitoring
- Days Since Filter Change — number of days since the last air filter change alarm
- Days To Filter Change — number of days remaining until the next filter change alarm
Output status monitoring
Eight boolean outputs indicate the current state of internal components:
- Hotgas Valve Heat and Hotgas Valve Cool — hotgas valve states for heating and cooling
- Condenser Close — air condenser inactive state
- Water Heater — hot water heater relay state
- Circulation Pump — EK circulation pump state
- Defrosting — defrost function active state
- Alarm Relay — alarm relay output state
- Pre-Heater — preheater or earth tube activation state
Two additional output sensors provide percentage values:
- Exhaust Fan Speed — exhaust fan speed
- Air Heater Capacity — air heater element capacity
Safety monitoring
- High Pressure Switch — high pressure safety trip status (true = pressure trip active)
Service mode
The Service Mode selector enables maintenance diagnostics with 9 sub-modes: Off, Defrost, Flaps, Inlet, Exhaust, Compressor, Heating, Hot Water, and Central Heat.
The Restart Mode indicator shows the external fire alarm reset mode (Off, HPLP, Continue).
Additional capabilities
The CTS-602 also exposes registers for 14 additional temperature sensors (outdoor, condenser, evaporator, inlet after heater, controller board, EK supply/return, and more), humidity and CO2 monitoring, alarm status and reset, writable ventilation step control, pressure sensors, air flow measurements, and extended configuration parameters. These can be added in a future template update.
The ventilation step is currently read-only in the template (reads from A:1100). To write the ventilation step directly, register H:1003 (Control.VentSet) can be added as a custom Modbus device in TapHome.
Troubleshooting
No Modbus communication
- Verify the RTU-to-TCP bridge is configured with the correct parameters: 19200 baud, 8 data bits, Even parity, 1 stop bit
- Check that the Slave ID in TapHome matches the CTS-602 setting (default 30)
- Confirm the RS-485 wiring — via 8-pole plug: pin 1 (GND), pin 6 (A1), pin 7 (B1); via CN7: pin 2 (Data+), pin 3 (Data-), pin 6 (GND)
- If communication fails, try swapping A and B lines — polarity can be reversed
- Verify the bridge device IP address is reachable from TapHome Core
- Check termination resistors (120 Ohm) at both ends of the RS-485 bus
Temperature readings show incorrect values
All temperature registers use a scale factor of 100. A raw value of 2200 means 22.00 °C. If values appear 100x too large or as raw integers, verify the template is correctly applied.
Mode changes not taking effect
The CTS-602 may not accept mode changes during certain states (e.g. defrost cycle, legionella heating). Wait for the current cycle to complete and try again. Check the Control State device for the current system state.
