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NTI · Boiler troubleshooting

No power - checking 120 VAC and 24 VAC at the boiler

Trinity Tft

What is going on

Nothing on the display or no response to a heat call; confirm the power supplies first.

Likely causes

  • Breaker tripped or service switch off
  • Front-of-boiler service switch off
  • No call from thermostat
  • Blown fuse (120 VAC fuse or 24 VAC fuse C)

Check in this order

  1. Confirm the breaker, any service switch and the switch on the front of the boiler are on
  2. Confirm the thermostat is calling and has 24 VAC
  3. Remove the front cover, then the control panel cover (three #8 screws)
  4. Measure 120 VAC across L1 and L2 (terminals 1 and 5); if absent trace the supply wiring
  5. If 120 VAC is there, shut power off and check the 120 VAC fuse on the control panel
  6. Measure 24 VAC between R and COM (terminals 1 and 2); if absent check the 24 VAC fuse at the transformer

Applies to: Trinity Tft60, Tft85, Tft110, Tft154, Tft201, Tft285, Tft340, Tft399

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Source: NTI Trinity Tft399 Installation and Operation Manual (2018-09-07), Sec. 16.0 Troubleshooting. Written in our own words; check the manual for your exact model.

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.