Lochinvar KNIGHT/FTXL boiler

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 only confirmed at the hardware-verified rung.

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
rate_command_setpoint_command	2	U16	1	HEX
tank_setpoint	3	U16	0.5	°C
tank_temperature	4	I16	0.1	%
outdoor_temperature	5	I16	0.1	%
system_supply_temperature	6	I16	0.1	%
dhw_recirculation_temperature	7	I16	0.1	°C

link settings as documented (unverified): RTU; baud 9600/19200; FC 01,02,03,04,05,06,07,08,11,12,15,16,17,23; Baud rate selectable with Dip switch #9 (9600 or 19200 bps). Parity selectable with Dip switch #10 (No Parity with 2 stop bits, or Even Parity with 1 stop bit). Modbus address (1-247) set via DIP switches 1-8.

⚠ This manual must only be used by a qualified heating installer / service technician. Read all instructions, including this manual, the Installation and Operation Manual, and the Service Manual, before installing. Perform steps in the order given. Failure to comply could result in severe personal injury, death, or substantial property damage. — Starkest reads only; we never write a control register.

bench facts as documented (unverified)

terminals	A, B, GND Shielded
A/B polarity	A + (positive), B - (negative)
termination	Cable must be terminated with 120 ohm impedance matching resistor on each end.
wiring notes	Maximum Length = 4000 feet. Cable Specification = 24 AWG / A,B (twisted pair) and GND Shielded, with characteristic Impedance = 120 ohm. Maximum Load = 32 units (32 nodes).
response timeout	10000 ms
broadcast	supported
protocol notes	The timeout is adjustable between 5 and 120 seconds. The default timeout is 10 seconds. Each message is started by at least 3.5 character times of silence. The maximum delay between frames is 1.5 character times. BAS must refresh commands at least every 4 minutes.
doc revision	MODB-I-O_100161545_2000014822_Rev N

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

To ensure proper operation, the configuration bits must be re-sent to holding register 40001 (or Object AV0) prior to issuing any command. If this is not done, the boiler may ignore subsequent commands. [source]
Integrators report difficulties writing to setpoints over BACnet/Modbus on Lochinvar boilers, sometimes requiring fallback to hardwired 0-10V setpoint control due to unreliable gateway behavior. [source]
confirmed: Baud rates [9600, 19200] and DIP switch settings (Dip switch #9 for baud rate, Dip switch #10 for parity, Dip switches 1-8 for address) — confirmed by Lochinvar Modbus and BACnet Communication Instructions manual (MODB-I-O_100161545_2000014822)
confirmed: Physical layer specifications (A/B/GND terminals, 120 ohm termination, 24 AWG cable, max 4000 ft, max 32 nodes) — confirmed by Lochinvar Modbus and BACnet Communication Instructions manual
confirmed: Polarity A + (positive), B - (negative) — confirmed by Lochinvar Modbus and BACnet Communication Instructions manual
confirmed: Supported Modbus function codes [1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 15, 16, 17, 23] — confirmed by Lochinvar Modbus and BACnet Communication Instructions manual
confirmed: Timing and timeout quirks (adjustable timeout 5-120s, default 10s, 3.5 character silence, 4-minute command refresh) — confirmed by Lochinvar Modbus and BACnet Communication Instructions manual
confirmed: Register map summary (0-based addresses 2 to 7 mapping to holding registers 40003 to 40008) — confirmed by Lochinvar Modbus and BACnet Communication Instructions manual

generated by gemini:gemini-3.5-flash · harvested from https://assets.lochinvar.com/damroot/Original/10014/810831MODB-I-O_100161545_2000014822_Rev%20N_FOR%20BACNET%20(40588).pdf (Lochinvar); manual-faithful — the document's claims, panel risk: ELEVATED — panel is not confident; proved interop-verified on 2026-06-10 · recorded 2026-06-10

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.

Have a device that isn't here? Upload its register map — generation is free, and the connector earns its rung by being proven, not claimed.

Need it proven on your own device? Hardware verification — if it doesn't verify, you don't pay.

Building a platform? License the verified library — machine-readable maps, firmware matrix, API access.