HVACopediaNTI · Boiler · Domestic hot water
Indirect tank (DHW) call
What happens, in order
- Tank aquastat (dry contact) closes SENSOR COM and DHW (terminals 6 and 9)
- Control turns on the DHW circulator output PUMP A
- In the single system circulator piping the CH circulator output PUMP C is turned off for the DHW call and PUMP B (boiler pump) stays on; with separate zone circulators PUMP A and PUMP C do the flowing and PUMP B is not used
- Control runs the ignition sequence
- Burner modulates to hold the DHW setpoint
- When the aquastat opens the burner shuts off, the blower post-purges and PUMP A drops out
Timings and thresholds
| Item | Value |
|---|---|
| DHW call input | Contact closure between terminals 6 and 9 |
Codes you may see during this
Hold / Lockout 79
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
- Circulator outputs and their fuses · Pump/purge
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.