Honeywell SOLA R7910 hydronic/steam control

Register map(s) for this device, each at the trust rung it earned. Addresses are 0-based as on the wire. Word order and scaling are confirmed at the hardware-verified rung and at no rung below it.

interop-verified

Read + decoded cleanly over a real network vs an independent third-party Modbus test server (transport and framing; reads are remapped into the server's register window, so the map's own addresses are NOT exercised). Does NOT prove word order/scaling against the actual device.

point	address (0-based)	type	scale	unit
status_change	0	U16	1
digital_io	2	U16	1
limits	4	U16	1
demand_source	6	U16	1
outlet_sensor_temp	7	U16	0.1	°C
firing_rate	8	U16	0.1	%
fan_speed	9	U16	1	RPM
flame_signal	10	U16	0.01	V
inlet_sensor_temp	11	U16	0.1	°C
dhw_sensor_temp	12	U16	0.1	°C
s5_sensor_temp	13	U16	0.1	°C
stack_sensor_temp	14	U16	0.1	°C
remote_control_input_ma	15	U16	0.1	mA
active_ch_setpoint	16	U16	0.1	°C
active_dhw_setpoint	17	U16	0.1	°C
active_ll_setpoint	18	U16	0.1	°C
steam_pressure	20	U16	0.1	psi
analog_modulation_input	21	U16	0.1	mA
active_ch_pressure_setpoint	22	U16	0.1	psi
active_ch_operating_point	25	U16	0.1	°C
active_dhw_operating_point	26	U16	0.1	°C
active_lead_lag_operating_point	27	U16	0.1	°C
active_system_operating_point	28	U16	0.1	°C
active_system_setpoint	29	U16	0.1	°C
burner_control_status	32	U16	1
burner_control_state	33	U16	1
lockout_code	34	U16	1
sequence_time	38	U16	1	s
delay_time	39	U16	1	s
burner_control_flags	41	U16	1
outlet_operation_temp	43	U16	0.1	°C
dhw_operation_temp	44	U16	0.1	°C
stack_or_heat_exchanger_operation_temp	45	U16	0.1	°C
ch_status	64	U16	1
ch_requested_rate	68	U16	0.1
dhw_status	80	U16	1
dhw_requested_rate	85	U16	0.1
burner_cycle_count	128	U32BE	1
burner_run_time	130	U32BE	1
ch_pump_cycle_count	132	U32BE	1
dhw_pump_cycle_count	134	U32BE	1
system_pump_cycle_count	136	U32BE	1
boiler_pump_cycle_count	138	U32BE	1
outdoor_temperature	170	U16	0.1	°C
outlet_t_rise_rate	172	U16	0.1	°C/s
exchanger_t_rise_rate	173	U16	0.1	°C/s
s10_sensor_reading	174	U16	0.1	°C

link settings as documented (unverified): RTU; default 38400 8N1; FC 03,06,16,17; RS-485 half duplex, LSB first, idle line for 3.5 or more characters.

bench facts as documented (unverified)

terminals	3-pin connector
A/B polarity	Terminal 1: Data + (a), Terminal 2: Data - (b), Terminal 3: Common (c)
connector	3-pin connector
wiring notes	MB1 or MB2 Modbus ports
max registers/read	125
sentinel values	0x8FFF for unconfigured temperature parameters, 0x7FFF or 0x8200 for no sensor configured, 0x8000 for shorted, 0x8100 for open, 0x8300 for outside high range, 0x8400 for outside low range, 0x8500 for not reliable.
protocol notes	Except for variable length data items, registers can be accessed as a single register or up to 20 registers for writes and 125 registers for reads. Variable length data must be accessed individually.
model register	176
firmware register	186
identification notes	Report Slave ID (FC17) returns OS number and Burner name. OS number is also at register 186, Burner name is at 183.
FC 43 device ID	not supported
doc revision	4.1.1

field reports — community-sourced, unverified (checked 2026-06-11)

Writing to any data register requires a password login (e.g., 'sola') to be written to register 177 (0x00B1) first, which remains in effect for only 10 minutes before another login is required. [source]
After a Modbus communication failure, the 'Comm Failure' alarm is not cleared until a successful write to both the Remote On/Off Modbus Command (00004) and Remote Firing Rate or Remote Setpoint (40006) points have been completed, or power is cycled. [source]
confirmed: Baud rate default of 38400, RTU framing, and half-duplex RS-485 comms — confirmed by Honeywell SOLA Software Interface Specification and Resideo R7910B User Manual
confirmed: Report Slave ID (FC17) returns OS number and Burner name — confirmed by Resideo R7910B User Manual
confirmed: OS number is at register 186 and Burner name is at register 183 — confirmed by CleaverBrooks CFC Operation Manual and CBT Tubeless Steam Boiler Manual
confirmed: Polarity of MB1/MB2 Modbus ports (Terminal 1/a: Data +, Terminal 2/b: Data -, Terminal 3/c: Common) — confirmed by CBT Tubeless Steam Boiler Manual
confirmed: Max read registers of 125 and write limit of 20 — confirmed by Honeywell SOLA Software Interface Specification
confirmed: Sentinel values (0x8FFF for unconfigured, 0x7FFF/0x8200 for no sensor, 0x8000 for shorted, 0x8100 for open, 0x8300/0x8400 for out of range, 0x8500 for unreliable) — confirmed by Honeywell SOLA Software Interface Specification

The trust ladder

Each rung states what it proved and what it did not. Gray until proven; green is earned by hardware only.

generated — A prompt produced it. Unproven — anyone can regenerate this.
structure-verified — Decode path is structurally sound (addresses, widths, finite values). Does NOT prove word order or scaling.
interop-verified — Read + decoded cleanly over a real network vs an independent third-party Modbus test server (transport and framing; reads are remapped into the server's register window, so the map's own addresses are NOT exercised). Does NOT prove word order/scaling against the actual device.
simulator-verified — Decoded correctly against a protocol emulator seeded with known-true values — catches word-order/scaling errors vs the emulator, not the physical device.
hardware-verified x1 — Matched a real device with operator-attested readings as ground truth — the only rung that confirms word order + scaling on the wire.

If your device isn't here, upload its register map. Generation is free, and the connector keeps the rung it earns under testing.

To prove a connector against your own device, order hardware verification. If it doesn't verify, you don't pay.

Platform builders can license the verified library: machine-readable maps, the firmware matrix, API access.