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NTI Error Code 5 P6: 3rd and 4th ignition failed (Boiler)

Updated · by Aurora Star Tech Inc.

NTI error code 5 P6 on a boiler means: 3rd and 4th ignition failed. It is also called NTI diagnostic code 5 P6.

High severityBoilerTRX

Homeowner? What NTI code 5 P6 means for you

Call a technician Your boiler is reporting: 3rd and 4th ignition failed. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.

Safe things you can check yourself

  • Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
  • Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
  • Look at the pressure gauge on the boiler. If it reads much lower than usual or near zero, or water is leaking, call a technician.
  • Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
  • Check that the boiler gas valve is open (handle in line with the pipe).
  • Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.

Call (647) 657-2977Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does NTI error code 5 P6 mean?

Third and fourth ignition attempts were unsuccessful. Warning.

Applies to: TRX150

Common causes of NTI code 5 P6

  • Gas pressure out of range
  • Faulty gas valve wiring
  • Faulty flame sensor

A technician checks these and 2 other possible causes on site before replacing any part.

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

NTI models that use code 5 P6

TRX085TRX110CTRX150TRX199TRX199C

Other NTI Boiler codes

CodeMeaning
05 01Ignition lockout after 3 failed attempts
05 02Flame detected with gas valve closed
05 0410 flame lifts in one operating cycle
5 P11st ignition failed
5 P22nd ignition failed
5 P3Flame loss during run
06 02Exhaust temperature above 204 °F (96 °C)
06 03APS open
06 05Exhaust NTC circuit open or short circuit
6 12Insufficient fan speed
Alert 1Alert PCB was restored from factory defaults
Alert 2Safety configuration parameters were restored from factory defaults

All NTI Boiler error codes →

NTI code 5 P6: homeowner questions

What does NTI code 5 P6 mean?

3rd and 4th ignition failed. Third and fourth ignition attempts were unsuccessful. Warning.

Is it safe to keep using my boiler with code 5 P6?

It depends on the cause. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.

Can I reset NTI code 5 P6 myself?

You can try one reset (power off for 30 seconds, then on). If NTI code 5 P6 comes back, the cause is still there and a licensed technician should check it.

Who can fix NTI code 5 P6 near me?

Aurora Star Tech Inc. repairs NTI boilers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.

Homeowner help: Boiler Not Heating: What to Check

Troubleshooting guides

Source: NTI TRX150 manual, p. 86. Written in our own words as a summary; always check the original manual.

General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.

© 2026 Aurora Star Tech Inc. All rights reserved. This page may not be copied, republished or used to train other systems without written permission.

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