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Lochinvar Modbus register maps

Updated 16 October 2026

2 Lochinvar models, 105 registers in all, each re-typed from Lochinvar’s own free documentation and checked against it.

• Boiler

  Lochinvar Crest / Crest with Hellcat boilers (ModBus communication board)

  Lochinvar Crest FB/OF 751-6001 and FCB1000-6000 (including Crest with Hellcat) with the ModBus communication board.

  62 registers · 9 writable · RTU
  Also known as: Crest, Crest FB751-6001, Crest OF751-6001, Crest FCB1000-6000, Hellcat, MTR-01
• Boiler / water heater

  Lochinvar Knight / Armor / Wall Mount boilers (ModBus communication board)

  Knight 81-286, Knight XL 400-1000, Armor 151-1000, Outdoor Knight/Knight XL/Armor, AQUAS 400-801, FTXL 400-1000, Wall Mount 51-211, Wall Hung 55-399, Wall Mount Armor 125-200 and Shield 125-500 with the Lochinvar ModBus communication board.

  43 registers · 11 writable · RTU
  Also known as: Knight, Knight XL, Outdoor Knight, Outdoor Knight XL, Armor, Outdoor Armor, Wall Mount Armor, Knight Wall Mount, Knight Wall Hung, AQUAS, FTXL, Shield

Lochinvar: default communication settings

Factory defaults as the manufacturer documents them. Change one setting at a time on site and write down what you changed. Word order applies to 32-bit values; the addressing column says how the manufacturer prints register numbers (every map on this site also gives the 0-based wire address).