HVACopediaNTI · Boiler · Heating
Central heat call (CH1) from call to satisfied
What happens, in order
- Thermostat or zone control closes R to CH1
- Boiler pump output PUMP B comes on (when the piping uses it) and the CH circulator output PUMP C comes on
- Water must flow through the boiler whenever the burner fires; check the minimum flow table
- Control runs the ignition sequence
- Burner modulates between minimum and maximum fan speed to chase the CH setpoint; with an outdoor sensor connected the setpoint follows outdoor reset (enabled from the factory)
- Fan speed can be held down by the outlet limit, delta-T limit, stack limit, anti-condensation logic or weak flame (Alerts 123 to 126, 449)
- Protective stops while running outlet high limit (200 F factory), delta T (81), stack limit (82, max 220 F), inlet/outlet inversion (85), outlet temperature rise (88)
- Call is satisfied when the thermostat opens or the outlet temperature rises above the setpoint plus the off hysteresis; burner shuts off and the blower post-purges
- Pump outputs drop out when the demand ends
Timings and thresholds
| Item | Value |
|---|---|
| Outlet high limit factory and maximum | 200 F (93 C) |
| Stack limit maximum | 220 F (104 C); 149 F (65 C) for PVC exhaust in Canada |
Codes you may see during this
Hold / Lockout 79, Hold / Lockout 81, Lockout 82, Hold / Lockout 85, Hold / Lockout 88, Alert 123, Alert 124, Alert 125, Alert 126, Alert 449
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
- Indirect tank (DHW) call · Domestic hot water
- Circulator outputs and their fuses · Pump/purge
Related
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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.