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NTI · Boiler troubleshooting

Primary/secondary piping for TRX150 / TRX199 with separate central heating circulator

TRX

What is going on

Use when the boiler's internal circulator cannot give enough flow to the secondary circuits.

Check in this order

  1. Pipe the heating loop as primary/secondary, with closely spaced tees within 4 pipe diameters centre to centre.
  2. Keep at least 6 pipe diameters of straight pipe upstream and downstream of closely spaced tees.
  3. Keep at least 12 pipe diameters of straight pipe upstream of every circulator.
  4. Use flow/check valves with weighted seats at or near the boiler where there is a single zone, to stop gravity circulation.
  5. Support the circulators separately; the piping does not carry their weight.
  6. Maintain at least 2 gpm through the heat exchanger to limit short cycling.
  7. Use a mixing valve on indirect water heater (IWH) applications if DHW is set above 119°F.

Applies to: TRX150 / TRX199 with multiple or single central heating circulators

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Source: NTI TRX150 manual, p. 32. 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.