HVACopedia

NTI · Boiler

06 05 Exhaust NTC circuit open or short circuit

Medium severity TRX

What the control is telling you

Exhaust temperature sensor circuit fault. Clears when fixed. Auto reset.

Applies to: TRX150

Likely causes

  • Wet or loose sensor connections
  • Very cold flue
  • Blocked exhaust vent

Test and repair steps

  1. Check the exhaust temperature sensor. Make sure the connections are dry and secure.
  2. If the flue is very cold, below 14 °F (-10 °C), remove the sensor, warm it, and reinstall it.
  3. If the flue is very hot, see code 602.
  4. Check the exhaust vent for blockages.

Models that show this code

5 models in TRX

TRX085TRX110CTRX150TRX199TRX199C

Other codes on the same units

  • 05 04 10 flame lifts in one operating cycle
  • 5 P1 1st ignition failed
  • 5 P2 2nd ignition failed
  • 5 P3 Flame loss during run
  • 5 P6 3rd and 4th ignition failed
  • 06 02 Exhaust temperature above 204 °F (96 °C)
  • 06 03 APS open
  • 6 12 Insufficient fan speed

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Source: NTI TRX150 manual, p. 87. Summarized in our own words; check the original manual for your model.

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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.