The fan coil displays an E7 fault code after connecting Modbus. What is wrong?

Parameter 9 (485 communication) on the device must be turned off. Leaving it enabled causes the E7 fault and prevents Modbus communication. Disable it from the unit screen, then retry.

I cannot read any registers even though the wiring looks correct. What should I check?

The A and B RS-485 pins on the fan coil PCB are swapped compared to the standard convention. Cross the A and B lines at the fan coil connector. Also verify the baud rate is set to 19200 with even parity on your gateway.

Can I use this template with Energy Save or Amitime branded fan coils?

Yes. According to the manufacturer documentation, the BM fan coil hardware is identical across HeizTech, Energy Save, Amitime, and other brands. The same template and register map apply.

The documented register addresses do not match the readings I see. Why?

The HeizTech documentation uses 1-based register addresses. Subtract one to get the zero-based address used in standard Modbus communication. The template already accounts for this offset.

Free Modbus template: BM fan coil unit - C series

Name: BM fan coil unit - C series
Brand: HeizTech
SKU: 609dbd69-f8cb-4c0d-9f50-5f000e513333

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Free Modbus template: BM fan coil unit - C series | ModbusCloud

Registers (15)

15 read / 13 write

Name	Address	Function	Type	Unit	Access
Setting mode 0—unit off;1—heating;2—cooling;3—air blow;4—dehumidification;5—auto	999	FC03	uint16		R/W
Set temperature range：16-31	1000	FC03	uint16	°C	R/W
Set air volume 0—fan stops;1—low speed;2—medium speed;3—high speed;4—auto;5—breeze	1001	FC03	uint16		R/W
Sleep function 0—off;1—on	1002	FC03	uint16		R/W
Relay 1 0—off, 1—on	1099	FC03	uint16		R/W
Relay 2 0—off, 1—on	1100	FC03	uint16		R/W
Fan speed range: 0-2500（r/min）	1101	FC03	uint16	rpm	R/W
Air inlet temperature Value = T *100 +3000	1199	FC03	uint16	°C	R
Water inlet temperature Value = T *100 +3000	1200	FC03	uint16	°C	R
Working mode 0: normal mode (bydefault);1: self-check mode(reserved);2: no logic mode	1899	FC03	uint16		R/W
Baud rate 0: 1200 (Invalid);1: 2400;2: 4800;3: 9600;4: 19200 (by default)	1900	FC03	uint16		R/W
Parity bit 0: NONE;1: EVEN (by default);2: ODD	1901	FC03	uint16		R/W
Stop bit 0: 1bit (by default);1: 1.5bit (invalid);2: 2bit	1904	FC03	uint16		R/W
Data bit 0：6bit (invalid);1：7bit (invalid);2：8bit (by default)	1905	FC03	uint16		R/W
Modbus address Range: 1-16; 1 bydefault	1923	FC03	uint16		R/W

BM fan coil unit - C series

Overview

Key readings

Available commands

Use cases

Installation

Things to watch for

Registers (15)

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