NTI Boiler Error Codes: LOC, ATT 7 and 101 Explained

Make one useful fault record

Use an accessible model label or the boiler paperwork. Write down the full model, all letters and numbers on the display, any words beside them, and whether the fault appeared during room heating or hot water use.

These are the manuals behind the sections below. The extra N in FTVN matters.

In these manuals, CH means central heating and DHW means domestic hot water. If your boiler has no code and simply keeps stopping, use boiler keeps turning off for that symptom.

Separate the service reminder from a fault

On the FTV models above, NTI says ATT 7 appears every 365 days as a service reminder. Arrange the service; the reminder itself does not name a failed component.

NTI clears it through setting 2-16, set to OFF, after servicing the boiler. That setting belongs to its Installer Menu, so leave it with the person doing the service.

The other FTV ATT messages in NTI’s table have different meanings:

For Att 3 or 4, NTI includes the hot water mode setting among the checks when no tank sensor is fitted. For Att 6 with an incorrect outdoor temperature reading, it directs the repairer to the outdoor sensor and its wiring. Those details matter before anyone orders a replacement sensor.

Find what caused the lockout

NTI uses Loc to say the FTV is locked out. The number alongside it identifies the condition. Its selected FTV entries below describe what the control detected, rather than telling you which part to buy.

For Loc 1, NTI’s checks include vent blockage, condensate drainage, gas pressure, ignition components and flame sensing. Tell the repairer whether it never lit or lit and immediately went out; the manual separates those two cases.

For Loc 5, NTI includes an external safety device such as a low water cutoff and bad connections in the safety circuit. Do not bridge a switch to get the heat back.

NTI says FTV hard lockouts such as Loc 1 and 2 cannot be cleared by switching the power off and on. Its reset method is to press and hold RESET on the display. Have the cause addressed first, especially for a safety circuit or unexpected flame indication.

Treat 101 as a temperature fault to investigate

In its FTVN Series II Rev. 10 chart, NTI prints 1 01 / 101 as outlet temperature exceeding 210 degrees F. The row is labelled Blocking (Manual Reset), so do not assume the word blocking means this particular code will clear itself.

NTI’s possible causes include air in the system, a plugged return filter, an internal pump that has failed or lost power, piping problems and faulty temperature sensors. The drawing shows why the investigation includes both water movement and temperature readings.

The same NTI row includes a tripped burner plate thermal switch. If that switch is open, the manual says not to operate the boiler and directs the technician to inspect the combustion chamber insulation. That is a reason to have 101 diagnosed before attempting a restart.

If you also have cold radiators, the boiler circulator pump guide explains that part of the system.

Keep the hold or lockout wording with the code

NTI’s April 2025 Trinity TFT manual and June 2024 FTG manual give the selected meanings below. These entries come from their hold and lockout charts, not their separate alert lists.

In the FTG troubleshooting chart, NTI calls Hold 61 normal operation and says to let its timer expire. It also describes Hold 62 appearing briefly before ignition as normal; a message that stays while the heat fails needs investigation.

For FTG 109, NTI’s service checks include the igniter, vent, condensate drain, gas supply and flame sensor connection. The number does not establish that the igniter itself has failed.

Notice the Disabled note beside 101 in the TFT and FTG lists. Do not use that entry to order an exchanger sensor or apply it to the FTVN Series II temperature fault above. If the boiler and chart do not agree, send the full fault record to the service company.