Overview

Ferroli Bluehelix Tech (25 kW) and Bluehelix HR (35 kW) are wall-hung condensing gas boilers with Modbus RTU capability via the optional Mod-RF communication module.

Mod-RF Installation

Mod-RF installation: clip Mod-RF module onto Bluehelix control board connector (right side, 10-pin header — see Ferroli Mod-RF Installation Manual section 3.2). Mod-RF must be activated by a certified Ferroli service partner (warranty condition). RS485 wiring: A, B, GND from Mod-RF terminal block to KNX Modbus gateway. Parameters: 19200 baud, 8N1, unit ID 1.

Register Map

Holding registers: 0 (operating status: 0=standby, 1=CH heating, 2=DHW, 3=frost protection, 4=alarm, read), 1 (flow temperature, int16, 0.1 degrees C, read), 2 (return temperature, read), 3 (DHW temperature, read), 4 (outdoor temperature if sensor fitted, read), 10 (CH flow setpoint, int16, 0.1 degrees C, write, range 200-800 = 20-80 degrees C), 11 (DHW setpoint, write, range 400-600 = 40-60 degrees C), 15 (boiler enable: 0=off, 1=on, write), 20 (burner modulation %, uint16, read).

MDT Modbus Gateway (SCN-MIG.01): configure read poll every 30s for all read registers. Write objects: register 10 (flow setpoint) and register 15 (enable).

KNX Weather Compensation Curve

Outdoor temperature sensor (Elsner KNX Tassino T UP, DPT 9.001) reads outdoor temp. KNX logic block applies the heating curve formula: setpoint = 80 - (outdoor_temp x 2.5) clamped to range 20-80 degrees C. Example: outdoor 0 degrees C → setpoint 80 degrees C (max), outdoor 15 degrees C → setpoint 42 degrees C (low load), outdoor 20 degrees C → setpoint 20 degrees C (pump off). The calculated setpoint is written to KNX GA → MDT Modbus Gateway writes to Bluehelix register 10. This modulating control improves condensing efficiency and comfort.

Night Setback, Fault Monitoring and DHW Boost

Night setback: KNX time switch (23:00-06:00) writes a reduced outdoor compensation setpoint (15 degrees C lower than daytime curve). Fault monitoring: register 0 value = 4 → KNX binary alarm object (DPT 1.005) → KNX push notification via Gira X1 or ETS-based notification. DHW boost: KNX binary output writes register 11 = 600 (60 degrees C setpoint) for legionella thermal disinfection once weekly — KNX timer triggers this on Sundays at 14:00.