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Primary/secondary piping and 3-way valve for heating-only use

TRX

What is going on

Piping rules for primary/secondary loops and the 3-way valve on TRX150/TRX199 models.

Check in this order

  1. Use primary/secondary piping when the boiler circulator does not give adequate flow to the secondary circuits.
  2. Keep closely spaced tees within 4 pipe diameters center to center, with 6 pipe diameters of straight pipe upstream and downstream.
  3. Keep at least 12 pipe diameters of straight pipe upstream of all circulators.
  4. Maintain at least 2 gpm through the heat exchanger to limit short cycling.
  5. If the boiler runs in heating mode only (no indirect water heater), cap the 3-way valve fitting.
  6. Disconnect the electrical connection of the 3-way valve motor while the boiler runs in central heating mode. Leaving it connected can disable freeze protection.

Applies to: TRX150, TRX199

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Source: NTI TRX150 manual, p. 26. 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.