NTI Boiler Error Codes — Meanings, Causes & Repair in Greater Vancouver

Seeing a fault code on your NTI boiler? This guide explains what the most common NTI boiler error codes mean, what’s safe to check yourself, and when to call HeatLand’s licensed, TSBC-certified gas technicians for NTI boiler repair across Metro Vancouver and the Fraser Valley.

The codes below apply across common NTI models (Trinity Tx, FTV, FTVN, Vmax, Trinity Lx). Meanings follow NTI’s documented fault codes — always confirm against your unit’s own manual, because exact wording can vary by model, control board and firmware.

How to read NTI boiler error codes

NTI's Argus display shows a 3-character prefix plus a number: 'Loc N' = hard lockout (safety; some require holding the RESET button to clear), 'Err N' = blocking/soft error (clears automatically when the fault is corrected), 'Att N' = attention/advisory, plus word codes 'FILL', 'Afro' (Anti-Frost), and 'tYPE' (appliance-type setup). Verified identical on the Trinity Tx and FTV Installation & Operation manuals; the Tx labels its main sensor 'Outlet/Clip-on' while the FTV labels the same sensor 'Supply'.

NTI boiler error codes & what they mean

These are the NTI boiler codes our Greater Vancouver technicians see most. Anything marked pro repair involves gas, electrical, sealed-combustion or control-board work that must be done by a licensed gas technician (TSBC-certified in BC) — never open gas or electrical components yourself.

Code	What it usually means	Common causes	Safe to check yourself
Loc 1	Ignition Error – five unsuccessful ignition attempts in a row (also shown as Loc 31 when flame is lost three times in one demand) pro repair	No or low gas supply / gas shut off or undersized line; Reversed 120VAC line polarity on a new install; Blocked vent or air intake	Confirm the gas supply valve to the boiler is open and other gas appliances work; Make sure power is on and the boiler is not in a manual off state; Check that the vent/intake terminals outside are clear of snow, ice, leaves, or nests
Loc 2 – 4	Gas Valve Circuit Fault (Safety) – the control sensed a fault in the gas valve electrical circuit (e.g. a loose gas-valve wiring-harness connection); may also indicate power-supply electrical interference pro repair	Loose or damaged gas valve wiring harness connection; Electrical noise / poor line-neutral-ground connections; Failed gas valve or controller	Confirm the boiler has clean, stable power (no shared circuit with welders, large motors, etc.); Press and release the RESET button once
Loc 5	Limit Circuit Open (Safety) – the control sensed a fault in the safety limit circuit (external limit/LWCO tripped, internal heat-exchanger thermal fuse open, or a bad connection in the limit circuit) pro repair	External limit device (e.g. low-water cutoff) tripped or miswired; Open heat-exchanger thermal fuse (Tx) – may require heat exchanger replacement; Bad electrical connection at J13 / limit wiring	If a low-water cutoff is fitted, confirm system pressure is in range (about 12-15 PSI) on the gauge; Press and release the RESET button once
Loc 6 & 7	Power Supply Electrical Interference – poor line, neutral or ground connections in the wiring to the boiler, internal ground problems, or electrical noise (may also point to Loc 5 limit-circuit issues) pro repair	Poor line/neutral/ground connections; Electrical noise from welders, large pump inverters, etc.; Power supplied by a generator without a proper UPS	Confirm the boiler is on a clean, dedicated power source and not sharing a circuit with noisy equipment; Press and release the RESET button once
Loc 8-9	Controller Malfunction – contact NTI, check field wiring, replace controller pro repair	Controller fault; Field wiring fault	Press and release the RESET button once
Loc 10	Supply/Outlet Sensor Fault – the control sensed an invalid reading at the supply (Tx: clip-on outlet) sensor; check cable then replace sensor pro repair	Failed or disconnected supply/outlet temperature sensor; Damaged sensor cable	Press and release the RESET button once
Loc 11	Uncorrected Blocking Error – a blocking error (Err) has lasted for 20 consecutive hours pro repair	An unresolved Err-code fault that was never corrected	Note any other Err code shown beforehand; Press and release the RESET button once
Loc 12	Incorrect Fan Speed – the measured combustion-fan speed did not reach target speed within 60 seconds; check fan wiring and the inline blower fuse pro repair	Loose fan wiring connection; Blown inline blower fuse; Failed combustion fan/blower	Press and release the RESET button once
Loc 13-24	Controller Malfunction – contact NTI, check field wiring, replace controller pro repair	Controller fault; Field wiring fault	Press and release the RESET button once
Loc 25	Outlet Sensor Detected Max Temp Reading / Limit Circuit Open – verify proper water flow through the boiler and test the outlet sensor and cable for a short; can also indicate a limit-circuit open or power-supply interference pro repair	Insufficient water flow through the boiler (air-bound, closed valve, failed pump); Shorted outlet sensor or cable; Limit-circuit fault / electrical interference	Confirm system pressure is about 12-15 PSI on the gauge; Confirm isolation valves to the boiler are open and the system pump is running; Press and release the RESET button once
Loc 26	Flue Sensor Fault – the control sensed an invalid reading at the flue sensor; check cable then replace sensor pro repair	Failed or disconnected flue temperature sensor; Damaged sensor cable	Press and release the RESET button once
Loc 27	Flame present 10 seconds after closing the gas valve – flame did not extinguish promptly after the burner demand ended pro repair	Faulty flame sensor; Blocked condensate drain; Post-purge setting too short	Confirm the condensate drain is clear and draining freely; Press and release the RESET button once
Loc 28	Flame present before ignition – flame was detected before the ignition sequence began pro repair	Faulty flame sensor; Blocked condensate drain; Post-purge setting too short	Confirm the condensate drain is clear and draining freely; Press and release the RESET button once
Loc 29-30	Controller Malfunction – contact NTI, check field wiring, replace controller pro repair	Controller fault; Field wiring fault	Press and release the RESET button once
Loc 31	Flame lost three times during one demand – treat the same as Loc 1 (ignition error) pro repair	Marginal gas supply / pressure; Dirty flame sensor; Vent/condensate restriction	Confirm the gas supply valve is fully open; Check vent/intake terminals and condensate drain are clear; Press and release the RESET button once
Loc 32 up	Controller Malfunction – contact NTI, check field wiring, replace controller pro repair	Controller fault; Field wiring fault	Press and release the RESET button once
Err 52	Incorrect Field Wiring – check electrical connections to the field terminal strip; ensure the thermostat is connected to terminals 7 and 8 pro repair	Thermostat or field wiring landed on the wrong terminals; Loose field terminal connection	Confirm the thermostat is calling/set correctly and has power; Press and release the RESET button once
Err 54	Flame detected out of sequence – flame sensed when none should be present; may also indicate water on the control board pro repair	Faulty flame sensor or flame-sensor wiring; Blocked condensate drain; Water on/in the controller	Confirm the condensate drain is clear and there is no obvious water leak onto the control; Press and release the RESET button once
Err 58-59	Water Pressure Error – increase system water pressure to a minimum of 12 PSI; if the gauge exceeds 15 PSI inspect/clean or replace the water pressure sensor pro repair	Low system water pressure / loss of water; Dirty or failed water pressure sensor; Air in the system	Read the system pressure gauge – it should be roughly 12-15 PSI when cold; If low, you may top up via the fill loop only if you are comfortable doing so; otherwise call a technician; Press and release the RESET button once
Err 60	Flue Sensor Error – flue temperature exceeded 205°F; the fan runs at minimum until flue temperature drops below 153°F. Often indicates the combustion chamber needs cleaning or the heat exchanger needs descaling pro repair	Dirty combustion chamber / scaled heat exchanger; Poor water flow; Failed flue sensor	Confirm system pressure is about 12-15 PSI and the pump is running; Allow the flue to cool and press RESET once; if it recurs, book service
Err 61	Return Sensor Error – inlet (return) temperature exceeded 203°F; clears when it drops below 190°F. Verify water flow, return-sensor reading and wiring pro repair	Insufficient water flow through the boiler; Air-bound system or failed circulator; Failed return sensor or wiring	Confirm system pressure is about 12-15 PSI on the gauge; Confirm isolation valves are open and the pump is running; Press and release the RESET button once
Err 64	Faulty Grounding – check appliance grounding to the breaker panel and the internal ground connections pro repair	Missing or poor earth ground to the boiler; Loose internal ground connection	Confirm the boiler breaker is on and power is stable; Press and release the RESET button once
Err 65	Incorrect Polarity – the control sensed reversed polarity of the 120VAC supply (line and neutral swapped at the field terminals) pro repair	Line and neutral reversed in the field wiring / at the receptacle; Wiring error during installation	Confirm the boiler is plugged into / wired to a correctly wired outlet; Press and release the RESET button once
Err 66	Incorrect Frequency – line frequency is outside 60Hz ±2%; if using a generator, install a UPS between the generator and boiler pro repair	Unstable line frequency; Generator power without a proper UPS	Confirm the boiler is on stable utility power, not unconditioned generator power; Press and release the RESET button once
Err 67	Faulty Earth Ground – check grounding of the boiler and power supply; replace controller if needed pro repair	Missing/poor earth ground; Failed controller	Confirm power is on and stable; Press and release the RESET button once
Err 72	Supply/Outlet Sensor Open – open circuit at the supply (Tx: clip-on outlet) sensor; check wiring then replace sensor pro repair	Disconnected or open supply/outlet sensor; Broken sensor wire	Press and release the RESET button once
Err 73	Supply/Outlet Sensor Fault – invalid supply (Tx: clip-on outlet) sensor reading; check wiring then replace sensor pro repair	Failed supply/outlet sensor; Damaged sensor wiring	Press and release the RESET button once
Err 78	Flue Sensor Open – open circuit at the flue sensor; check wiring then replace sensor pro repair	Disconnected or open flue sensor; Broken sensor wire	Press and release the RESET button once
Err 80	Supply/Outlet Sensor Shorted – short circuit at the supply (Tx: clip-on) sensor; check wiring then replace sensor pro repair	Shorted supply/outlet sensor; Pinched/damaged sensor wiring	Press and release the RESET button once
Err 81	Supply/Outlet Sensor Shorted – short circuit at the supply (Tx: clip-on) sensor; check wiring then replace sensor pro repair	Shorted supply/outlet sensor; Pinched/damaged sensor wiring	Press and release the RESET button once
Err 86	Flue Sensor Shorted – treat the same as Err 60 (flue sensor error / over-temperature) pro repair	Shorted flue sensor or wiring; Dirty combustion chamber / scaled heat exchanger	Allow the flue to cool and press RESET once; if it recurs, book service
Err 87	Reset Button Error – the control sensed that the RESET button is stuck; inspect and try pressing/releasing it to free it pro repair	Physically stuck RESET button; Plastic display overlay binding the button; Failed display	Gently press and release the RESET button a few times to free it; Turn the boiler power off and back on once
Err 93	Appliance Type – the appliance type stored in the display does not match the appliance type stored in the controller; the correct type must be set (typically after a control/display replacement) pro repair	Recent controller or display replacement not yet configured; Appliance Type setting mismatch	Note that this usually follows a parts replacement and needs a technician to set the appliance type
Att 2	Outdoor Sensor Shorted – short circuit at the outdoor sensor; check the wiring to terminals 3 and 5 and the outdoor sensor pro repair	Shorted outdoor air sensor; Damaged outdoor sensor wiring	No safe homeowner check beyond noting the code; boiler typically still heats
Att 3	DHW Sensor Open – open circuit at the domestic-hot-water tank sensor; check wiring to terminals 3 and 6 and the tank sensor (or set DHW Mode if no tank sensor is used) pro repair	Disconnected/open DHW tank sensor; DHW Mode set incorrectly when no tank sensor is fitted	Note the code; this is advisory and usually does not stop space heating
Att 4	DHW Sensor Shorted – short circuit at the DHW tank sensor; check wiring to terminals 3 and 6 and the tank sensor (or set DHW Mode if no tank sensor is used) pro repair	Shorted DHW tank sensor or wiring; DHW Mode set incorrectly when no tank sensor is fitted	Note the code; this is advisory and usually does not stop space heating
Att 6	Warm Weather Shutdown (WWSD) Active – the outdoor temperature exceeds the WWSD setting, so central heating is suspended and the boiler responds only to DHW demands. This is normal seasonal behavior, not a fault DIY-checkable	Outdoor temperature above the WWSD setpoint (normal in mild/warm weather); WWSD setpoint set too low; Faulty outdoor sensor reading	Understand this is expected when it is warm outside and heat is not needed; No reset required; heating resumes when it cools
Att 7	Service Reminder – occurs every 365 days; the boiler is due for service. Clear by setting menu 2-16 to OFF after servicing pro repair	Annual service interval reached	Schedule annual professional maintenance; the reminder does not stop the boiler from running
FILL	Low Water Pressure – increase system water pressure to a minimum of 12 PSI; if the gauge exceeds 15 PSI, inspect/clean or replace the water pressure sensor pro repair	Low system water pressure / gradual water loss; Air in the system; Dirty or failed water pressure sensor	Read the system pressure gauge – it should be about 12-15 PSI when cold; Top up via the fill loop only if you are comfortable doing so; otherwise call a technician; Press and release the RESET button once once pressure is restored
Afro	Anti-Frost (Frost Protection) – not a fault; shown when the boiler senses supply/return temperature below ~50°F and runs the pumps (and burner below ~41°F) to protect against freezing until temperatures recover to ~60°F DIY-checkable	Very cold boiler/water temperature triggering built-in freeze protection (normal)	No action needed; this is automatic freeze protection and clears on its own as the boiler warms

NTI boiler codes we get called for most

Loc 1 — Ignition Error – five unsuccessful ignition attempts in a row (also shown as Loc 31 when flame is lost three times in one demand)

Typical causes include no or low gas supply / gas shut off or undersized line; reversed 120vac line polarity on a new install; blocked vent or air intake. A few things are safe to check yourself (Confirm the gas supply valve to the boiler is open and other gas appliances work; Make sure power is on and the boiler is not in a manual off state), but the repair is a licensed, TSBC-certified gas technician job. HeatLand diagnoses and fixes Loc 1 on NTI boilers throughout Greater Vancouver.

Loc 31 — Flame lost three times during one demand – treat the same as Loc 1 (ignition error)

Typical causes include marginal gas supply / pressure; dirty flame sensor; vent/condensate restriction. A few things are safe to check yourself (Confirm the gas supply valve is fully open; Check vent/intake terminals and condensate drain are clear), but the repair is a licensed, TSBC-certified gas technician job. HeatLand diagnoses and fixes Loc 31 on NTI boilers throughout Greater Vancouver.

Err 58-59 — Water Pressure Error – increase system water pressure to a minimum of 12 PSI; if the gauge exceeds 15 PSI inspect/clean or replace the water pressure sensor

Typical causes include low system water pressure / loss of water; dirty or failed water pressure sensor; air in the system. A few things are safe to check yourself (Read the system pressure gauge – it should be roughly 12-15 PSI when cold; If low, you may top up via the fill loop only if you are comfortable doing so; otherwise call a technician), but the repair is a licensed, TSBC-certified gas technician job. HeatLand diagnoses and fixes Err 58-59 on NTI boilers throughout Greater Vancouver.

Err 86 — Flue Sensor Shorted – treat the same as Err 60 (flue sensor error / over-temperature)

Typical causes include shorted flue sensor or wiring; dirty combustion chamber / scaled heat exchanger. A few things are safe to check yourself (Allow the flue to cool and press RESET once; if it recurs, book service), but the repair is a licensed, TSBC-certified gas technician job. HeatLand diagnoses and fixes Err 86 on NTI boilers throughout Greater Vancouver.

Is it safe to keep running a NTI boiler with a fault code?

Most NTI fault codes put the boiler into a safe lockout for a reason. You can safely check the basics — gas supply on, power on, the thermostat calling for heat, system pressure in the normal range, and the condensate drain not frozen or blocked (a common cause in Vancouver cold snaps) — and restart it once. If the code returns, stop and book a technician. If you ever smell gas, leave the building and call your gas utility’s emergency line or 911 first. If a carbon-monoxide alarm sounds, get everyone out and call 911.

NTI boiler repair across Greater Vancouver

HeatLand has kept Metro Vancouver homes comfortable since 1999. Our licensed, insured technicians diagnose and repair NTI boilers — ignition faults, flame and sensor errors, low-pressure and pump problems, fan and flue faults, and control-board issues — including units we didn’t install. We’re brand-agnostic, carry common parts, and give you an honest repair-or-replace assessment with upfront pricing and a free estimate. If your boiler is beyond economical repair, we’ll show you right-sized, high-efficiency replacement options and the rebates available.

Need it sorted fast? We offer priority emergency boiler repair. Explore Boiler services, browse all boiler error codes by brand, or request a free estimate.

NTI boiler service areas

We repair NTI boilers across Greater Vancouver and the Fraser Valley, including:

NTI boiler error code FAQs

Can I reset my NTI boiler myself?

Yes — power-cycling the reset button once is generally safe after you’ve checked the basics (gas supply on, power on, the thermostat calling for heat, system pressure in the normal range, and the condensate drain not frozen or blocked (a common cause in Vancouver cold snaps)). If the boiler faults again right away, stop and note the code — repeatedly resetting a boiler that keeps locking out can mask a real problem. Call a licensed, TSBC-certified gas technician to diagnose it.

What does the NTI Loc 1 code mean?

On NTI boilers, Loc 1 commonly indicates ignition error – five unsuccessful ignition attempts in a row (also shown as loc 31 when flame is lost three times in one demand). Confirm the exact meaning against your unit’s manual — codes can vary by model and series — and have the repair done by a licensed, TSBC-certified gas technician. HeatLand fixes this across Greater Vancouver.

Do you repair NTI boilers you didn’t install?

Yes. HeatLand is brand-agnostic and services NTI boilers throughout Metro Vancouver and the Fraser Valley, whether or not we installed the unit. We carry common parts and give you an honest repair-or-replace assessment.

Is a NTI boiler fault code an emergency?

No heat in cold weather is worth treating urgently. If you ever smell gas, leave the building and call your gas utility’s emergency line or 911 first. If a carbon-monoxide alarm sounds, get everyone out and call 911. For priority boiler repair across Greater Vancouver, call (604) 330-3812.

How much does NTI boiler repair cost in Vancouver?

It depends on the fault. Many NTI codes point to sensors, ignition or pump parts — usually far cheaper than replacement. We give upfront pricing and a free estimate before any work.

More Boiler error-code guides

HeatLand repairs every major boiler brand across Greater Vancouver. More brand guides: