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NTI Error Code 02 03: Storage temperature probe open or short circuit (Boiler)

Updated · by Aurora Star Tech Inc.

NTI error code 02 03 on a boiler means: Storage temperature probe open or short circuit. It is also called NTI diagnostic code 02 03.

Medium severityBoilerTRX

Homeowner? What NTI code 02 03 means for you

Check, then call Your boiler is reporting: Storage temperature probe open or short circuit. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.

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 02 03 mean?

Applies to Non-Combi boilers with a DHW tank sensor. CH demand continues to run.

Applies to: TRX150 (Non-Combi with tank sensor)

Common causes of NTI code 02 03

  • Damaged tank sensor or wiring
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 02 03

TRX085TRX110CTRX150TRX199TRX199C

Other NTI Boiler codes

CodeMeaning
1 14External (outdoor) sensor open or short circuit
1 16Floor thermostat contact open
1 P1Insufficient circulation or missing water (warning)
1 P2Insufficient circulation or missing water (warning)
1 P3Inadequate circulation or missing water (warning)
02 01Damaged or shorted DHW temperature probe
02 05DHW inlet probe open circuit
02 09Storage overheating
2 P2Anti-Legionella function not completely finished
03 01Display EEPROM error
03 02Communication error GP-GIU
03 03PCB internal error

All NTI Boiler error codes →

NTI code 02 03: homeowner questions

What does NTI code 02 03 mean?

Storage temperature probe open or short circuit. Applies to Non-Combi boilers with a DHW tank sensor. CH demand continues to run.

Is it safe to keep using my boiler with code 02 03?

It depends on the cause. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.

Can I reset NTI code 02 03 myself?

You can try one reset (power off for 30 seconds, then on). If NTI code 02 03 comes back, the cause is still there and a licensed technician should check it.

Who can fix NTI code 02 03 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. 91. 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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