The Nilan CTS-602 Air Recovery template is designed for Nilan’s Comfort 250, Comfort 300, Comfort 300 Top, Comfort CT300, Comfort 450 and Comfort 600 series ventilation units with heat recovery. These are HRV (heat recovery ventilation) units controlled by the CTS-602 controller. The TapHome template connects to the CTS-602 via Modbus TCP, providing temperature setpoint control, ventilation step control, humidity monitoring, operating mode selection and electric boiler switching.
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.
This is the Air Recovery variant of the CTS-602 template with 6 devices focused on core ventilation and climate control. The Nilan CTS-602 Heat Pump template for the same controller exposes 38 devices including additional temperature sensors, output status monitoring and hot water management.
Hardware connection
The Modbus RS-485 interface is available on the 6-pin CN7 connector (next to the USB plug) directly on the CTS-602 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.
On Comfort 250/300/300 Top/450/600 models with the older knob-based panel, the Modbus wires can also be accessed through the 8-pole connector plug on top of the unit (pin 6 = A1/Data+, pin 7 = B1/Data-, pin 1 = GND).
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.
Enabling Modbus communication
The Modbus interface is always active on the CTS-602 — 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, enter the SERVICE menu on the CTS-602 control panel:
- Press Down + ENTER simultaneously for 10 seconds to activate the service menu
- Press Down multiple times until the panel shows SERVICE, then press ENTER
- Scroll down through the menu items (HEATING SURFACE, AIR QUALITY, AIR EXCHANGE, DEFROST, TEMP. CONTROL, INLET CONTROL, ROOM CONTROL, RESTART, RESET, MANUAL, PWR SAVE) until you reach MODBUS ADR 30
- Press ENTER to edit the address, use Up/Down to change the value, then press ENTER to confirm
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.
TapHome import parameters
When importing the template, TapHome prompts for:
- Slave ID — default 30 in template, change to match the CTS-602 setting if modified
- IP Address — the IP address of the RTU-to-TCP bridge device
Device capabilities
Temperature control
The Temperature Setpoint thermostat device reads the current room temperature from the T15 user panel sensor (A:215) and writes the desired temperature setpoint to H:1004. It also reads humidity from the built-in humidity sensor (A:221). All temperature values use a scale factor of 100 (register value 2200 = 22.00 °C).
Humidity monitoring
The Humidity sensor reads the indoor humidity value from A:221 (AirQual.RH), displayed as a percentage. This is useful for indoor air quality monitoring and can be used in TapHome automations to trigger ventilation speed changes.
Operating mode control
The Mode Set selector controls the operating mode via H:1002 with the following values:
- 0 = Off
- 1 = Heat
- 2 = Cool
- 3 = Auto
- 4 = Service
Ventilation control
The Ventilation Level Set device provides read/write control of the ventilation fan step via H:1003 (Control.VentSet):
- 0 = Off
- 1-4 = Ventilation step (corresponding to the fan speed percentages configured in the CTS-602 AIR EXCHANGE service menu)
The Inlet Fan Speed device reads and writes the inlet fan speed as a percentage of maximum capacity via H:201 (Output.InletSpeed), with a scale factor of 100.
Electric boiler control
The Electric Boiler switch controls the EK heater relay (H:119, Output.CenHeat_1) for units equipped with an electric heating element. This is a simple on/off switch.
Additional capabilities
The CTS-602 controller exposes many more registers that can be added in a future template update, including:
- Temperature sensors T0-T8 (controller board, intake, inlet, exhaust, outlet, outdoor temperatures)
- Run state and control state monitoring (A:1000, A:1002)
- Filter change counters (A:1103, A:1104)
- Heat exchanger efficiency (A:1204)
- Exhaust fan speed (H:200)
- CO2 sensor (A:222)
- Alarm status and reset (A:400, H:400)
- Service mode control (H:1005)
For a more comprehensive template with 38 devices including all temperature sensors, output status monitoring and hot water management, see the Nilan CTS-602 Heat Pump template. Both templates use the same CTS-602 controller and can be used on the same hardware — choose the one that best fits your unit type and monitoring needs.
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 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.
Ventilation step changes not taking effect
The CTS-602 may override the ventilation step setting during certain conditions (e.g. humidity-controlled ventilation, low outdoor temperature reduction, or alarm states). Check the AIR QUALITY and AIR EXCHANGE settings in the service menu. If humidity or CO2 regulation is enabled, the controller may automatically increase or decrease fan speed regardless of the Modbus setting.
