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NTI Error Code Lockout 252: Invalid Line frequency setting (Boiler)

Updated · by Aurora Star Tech Inc.

NTI error code Lockout 252 on a boiler means: Invalid Line frequency setting. It is also called NTI diagnostic code Lockout 252.

High severityBoilerTrinity Tft

Homeowner? What NTI code Lockout 252 means for you

Call a technician Your boiler is reporting: Invalid Line frequency setting. 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 Lockout 252 mean?

The control rejected a configuration value: invalid Line frequency setting.

Applies to: Trinity Tft60, Tft85, Tft110, Tft154, Tft201, Tft285, Tft340, Tft399

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 Lockout 252

Tft60Tft60Tft85Tft85Tft110Tft110Tft154Tft155Tft175Tft200Tft201Tft250Tft285Tft300Tft340Tft399Tft399

Other NTI Boiler codes

CodeMeaning
Lockout 2464-20mA cannot be used for both modulation and setpoint control
Lockout 247Invalid ILK bounce detection enable
Lockout 248Invalid forced recycle interval
Lockout 249STAT cannot be demand source when Remote Stat is enabled
Lockout 250Invalid Fan speed error response
Lockout 251Lead drop-stage on error setting does not match drop method configuration
Lockout 253Lead Lag modulation sensor not valid with setpoint source
Lockout 254Lead Lag modulation sensor not valid with local setpoint source
Lockout 255Lead Lag modulation sensor not valid with local modulation source
Lockout 256Selected Controller interaction enable setting is not allowed
Lockout 257Controller interaction enable does not match neighbor stack fault setting
Lockout 258Controller ID must be non-zero if controller interaction is enabled

All NTI Boiler error codes →

NTI code Lockout 252: homeowner questions

What does NTI code Lockout 252 mean?

Invalid Line frequency setting. The control rejected a configuration value: invalid Line frequency setting.

Is it safe to keep using my boiler with code Lockout 252?

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 Lockout 252 myself?

You can try one reset (power off for 30 seconds, then on). If NTI code Lockout 252 comes back, the cause is still there and a licensed technician should check it.

Who can fix NTI code Lockout 252 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 Trinity Tft399 Installation and Operation Manual (2018-09-07), Sec. 16.0 Troubleshooting, Table 16-3. 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.

Emergency Boiler Repair

647-657-2977