HVACopediaNTI · Boiler · Other
Lead-lag (cascade) demand handling
What happens, in order
- Up to 8 boilers share a primary/secondary loop and are linked by three-wire communication (DATA+, DATA-, DATA COM)
- One boiler is set as master and becomes the single contact point for central heat and outdoor reset settings and system control wiring
- Central heat call from the master's CH2 (LL) input; the system sensor, when fitted, becomes the modulation sensor
- The master stages the other boilers and each boiler runs its own boiler pump from PUMP B
- One boiler can run the shared CH pump on PUMP C and one the DHW pump on PUMP A for master demands
- Each boiler must have its own Modbus address from 1 to 8
Codes you may see during this
Applies to: Trinity Tft60, Tft85, Tft110, Tft155, Tft175, Tft200, Tft250, Tft300, Tft399
Models
More NTI boiler sequences
- Combustion checking procedure · Startup
- Power-on and mode sequence · Startup
- Power-up and what lets the boiler start a call · Startup
- Failed ignition and lockout · Ignition
- First ignition start-up · Ignition
- Light-off sequence and retries · Ignition
- Central heat call (CH1) from call to satisfied · Heating
- Indirect tank (DHW) call · Domestic hot water
Related
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Sequences of operation, error codes and tips work offline in the HVACopedia app.
Source: NTI Tft60-399 Installation and Operation Instructions (rev. 2012-04-09), Sec. 8.0 Lighting, Sec. 10.0 Piping, Sec. 15.0 Troubleshooting. Written in our own words; timings can differ by model and software version, so check the manual for your exact unit.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.