Start by identifying the control: the Trinity Ti (Ti100 to Ti400) carries the Sentry 2100, a small digital readout that normally shows water temperature and swaps to ER and a digit, or to the letters ASO, when something is wrong. Older paperwork calls the manufacturer NY Thermal, which is the same company. The Trinity Tft, the Lx and the FTG have a colour touchscreen with a Honeywell Sola controller behind it, and the boiler icon on the home page changes colour: blue is normal, yellow is a Hold, red is a Lockout. The Trinity Tx and the FTV have a smaller screen that prints Loc or Err in the top-left corner with a number beside it.
On the Sola, the word in front of the number matters as much as the number. A Hold means the controller has paused the burner and is waiting for a condition to clear or a timer to run out, then it tries again by itself. A Lockout means it has given up and will not fire until someone resets it at the boiler's power switch, the RESET button on the controller, or the Clear Lockout button on the touchscreen History page. Alerts are a third category, logged for information only, and the History page keeps the last fifteen Lockouts and the last fifteen Alerts.
Several faults carry both labels: NTI's chart lists Lockout or Hold 79 and Lockout or Hold 81, because installer settings decide whether a limit recycles or locks. Codes vary by model and by software version, and NTI's installation manual for your model, along with the label inside the cabinet, wins over this page. The Sola is also used by other boiler makers with their own wiring, so do not carry these meanings to another brand. See the NTI boiler repair page for the lines we service, the IBC code guide if the neighbouring unit is an IBC, or the brands hub for everything else.
NTI boiler codes, decoded
| Code | What it means | Safe? | Try first | When to call |
|---|---|---|---|---|
ER1 (Sentry) | Safety high limit reached. The Sentry has read an excessive water temperature at its sensor; the Ti manuals we checked put it at about 121°C. | turn it off | Check the pressure gauge reads at least 12 psi and that zone valves or radiator valves are open. | Same day. Water is not moving through the boiler, and NTI asks to be contacted if the boiler is extremely hot. |
ER2 / ER3 (Sentry) | Water sensor short circuit (ER2) or open circuit (ER3). NTI notes ER3 also appears if the sensor reads below freezing. | turn it off | If the boiler room has been unheated, warm the space before assuming a failed part. | Book a repair. The sensor and its wiring are tested for resistance and for water dripping onto the probe. |
ER4 (Sentry) | 24-volt limit error. A safety in the limit string, such as the water pressure or flow switch, is open. The Ti manual says the boiler waits one hour and retries. | turn it off | Read the pressure gauge. A loop that has sagged well below 12 psi opens the pressure switch. | If pressure is normal or will not hold. The open device is found by checking continuity along the limit circuit. |
ER5 (Sentry) | Indirect water heater problem. The domestic hot water call ran too long or cycled the boiler off repeatedly; the exact trigger changed between Sentry versions. | keep running | Turn the indirect tank's aquastat down slightly and switch boiler power off and on to clear it. | If it keeps coming back. Flow through the indirect circuit or the tank's own limit needs checking. |
ER6 (Sentry) | Flame lockout. The Sentry lost 24 volts to the gas valve during operation, or the Fenwal ignition module locked out. | turn it off | Confirm the gas is on and the vent terminations outside are clear of snow. | Same day. Igniter, flame sensor, gas valve and limit trips are each tested in the ignition sequence. |
ASO / ASC (Sentry) | Air switch open (ASO) while the blower runs, or air switch closed (ASC) after the blower stops. A brief ASO at start-up is normal. | turn it off | Look for ice, snow or debris at the intake and exhaust pipes outside. | If ASO stays on the display. The vinyl sensing tube, the vent run and the fan are the three suspects. |
Hold 61 (Sola) | Anti short-cycle. A timer is stopping the burner from relighting too soon after it shut off. | keep running | Wait. NTI lists this as normal operation. | Not needed, unless the boiler short-cycles all day, which is a sizing or setup conversation. |
Hold 62 (Sola) | Fan speed not proved. It flashes briefly before every ignition; it is a fault only when it persists for 15 seconds or more. | keep running | Nothing if it passes in a moment. | If it sticks. NTI's chart goes to Fuse A, the blower wiring and then the blower itself. |
Hold / Lockout 67 (Sola) | ILK OFF. The interlock string is open: a low water condition at the internal low water cutoff, or an external limit wired to the boiler has tripped. | turn it off | Check system pressure and look for the amber LOW WATER light on the cutoff module. | Same day. Refilling, purging air and finding why water was lost come before any reset. |
Lockout or Hold 79 (Sola) | Outlet high limit. Outlet water passed the limit setpoint, 93°C from the factory on the Tft, which ships set to recycle and hold instead of locking out. | turn it off | Open any closed zones or radiator valves so the boiler has somewhere to send heat. | If it repeats. Setpoints stacked too close to the limit, or a pump that has stopped, are NTI's listed causes. |
Lockout or Hold 81 (Sola) | Delta-T limit. Outlet water is more than 60°F (about 33°C) hotter than inlet. The Sola allows the first cycle and two recycles, then locks out. | turn it off | Listen for banging or hissing from the boiler and check the gauge shows at least 15 psi. | Book a repair. Insufficient flow: Fuse B, the boiler pump, the piping, or an exchanger fouled with scale or magnetite. |
Lockout 82 (Sola) | Stack limit. Flue gas at the exhaust port is over the setpoint. In Canada the setpoint is held to 65°C on PVC exhaust venting. | call now | Switch the boiler off and leave it off. | Immediately. A dirty heat exchanger is the listed cause, and overheated plastic venting is a safety matter. |
Hold 91 / 92 / 95 (Sola) | Inlet sensor (91), outlet sensor (92) or stack sensor (95) fault: disconnected or failed. | turn it off | Nothing at home. | Book a repair. Each sensor is unplugged and its resistance compared with NTI's thermistor chart. |
Lockout 108 (Sola) | Flame lost in run. Listed in Honeywell's Sola fault table: the burner was established and the flame signal dropped out. | turn it off | Check outside for a blocked or iced vent termination. | Same day. Flame rod condition, gas pressure under load and combustion settings all need instruments. |
Lockout 109 / Hold 110 (Sola) | Ignition failure occurred: no flame proved after three ignition attempts. Whether it shows as 109 or 110 depends on the lockout or recycle setting. | turn it off | Confirm the manual gas valve is open and the condensate drain hose is not kinked or frozen. | After one failed reset. Spark cable, electrode, flame rod, spark generator and gas valve are checked in that order. |
Lockout 138 (Sola) | Flame too low. The flame signal fell below what the controller will accept. | turn it off | Nothing beyond checking the vent terminations. | Book a repair. Blocked venting, a fouled flame sensor or combustion settings that have drifted. |
Alert 248 (Sola) | CH outdoor temperature was invalid. The Tft ships with outdoor reset enabled and is not seeing its outdoor sensor. | keep running | Clear ice and snow off the outdoor sensor and check its wire. | At the next service. The sensor is connected properly or outdoor reset is disabled. |
Alert 448 / 449 (Sola) | Flame too low (448), or modulation rate limited due to flame strength (449). Early warnings that sit in the Alert history. | keep running | Note how often they appear in the History page. | Soon if they repeat. NTI refers both to the Lockout 138 checks before the boiler starts locking out. |
Loc 1 (Tx / FTV) | Ignition error after repeated unsuccessful ignition attempts in a row. A hard lockout: cycling the power does not clear it. | turn it off | Press and hold the RESET button on the display once, after checking the gas is on. | If Loc 1 returns. Venting, condensate trap, gas pressure, flame sensor and spark electrode are the manual's list. |
Fill (Tx) | Low water pressure. Below 7 psi the Tx stops the burner until pressure is restored. | turn it off | Read the pressure on the display and look for a leak or a dripping relief valve. | If it will not stay above 12 psi after filling. The expansion tank or a leak is behind it. |
The codes that usually mean a real repair
Lockout 109, Hold 110, ER6 or Loc 1: ignition
Repeated ignition lockouts on an NTI are a service job, not a reset job: the spark electrode erodes and its gap opens up, the flame rod grows an oxide coating that weakens the signal, and the burner and condensate trap collect debris that upsets combustion. Resetting gets a few more lights out of a tired electrode and then stops working, usually on the coldest night. The fix is to pull the burner door, clean or replace the electrode and flame rod, clear the trap and set combustion with an analyzer, which only a licensed gas technician may do. There is no kit price for boiler ignition parts, so you get a written quote after a $90–$150 diagnostic that is folded into the repair.
Hold 81, Hold 79 or ER1: water is not moving
Delta-T and high-limit codes mean the burner is making heat faster than the water carries it away. NTI's chart starts with Fuse B and the boiler pump, then piping, then system pressure, then an exchanger fouled with scale or magnetite. In older Hamilton and Burlington houses with cast-iron radiators, black magnetite sludge from the old system is a common finding on a boiler that was never flushed at install. Why a boiler keeps shutting off covers the symptoms, and the repair ranges from a pump to a full system clean, quoted in writing.
ASO, Lockout 82 or Alert 448: vent, trap and heat exchanger
These three point at the air and flue path. A Ti showing ASO has an air-proving switch that will not close, a Sola boiler on Lockout 82 has flue gas running too hot, and repeated 448 alerts say the flame signal is fading. Ice on a side-wall termination after a freeze-thaw week near Lake Ontario, a condensate trap packed with sediment and a combustion chamber that has not been cleaned in years account for most of them. Clearing a blocked condensate trap or drain is typically $150–$350; a heat exchanger clean is part of a proper annual service under boiler repair and maintenance.
Licensed technicians, a written price before the repair, no overtime charges.
Common questions
What is the difference between a Hold and a Lockout on an NTI boiler?
A Hold is temporary. The Sola controller stops the burner, waits for a timer or for a reading to return to range, and restarts without anyone touching it. A Lockout is final until a person resets it. Holds that repeat are worth noting because several, including 110 and 81, turn into Lockouts once the allowed retries are used up.
How do I reset a Lockout on a Trinity Tft?
NTI gives three ways: switch the boiler's own power switch off and on, press the RESET button on the Sola controller inside the cabinet, or open History on the touchscreen and press Clear Lockout. Use the touchscreen so you can read the fault first. Reset once; if the same number returns, contact us with the code and the History list.
Why does my Trinity Ti show ASO for a second and then run fine?
That is expected. The Sentry displays ASO whenever it wants the air switch closed and has not seen it close yet, which includes the moment the blower spins up. NTI's manual says a momentary ASO is normal and a persistent one is a fault. If the letters stay on and the burner never lights, look at the vent pipes outside before calling.
Is my NTI boiler a Sentry or a Sola model?
A small numeric readout with a few indicator lights is the Sentry 2100 on a Trinity Ti. A colour touchscreen with a boiler icon is the Sola on a Tft, Lx or FTG. A compact display that shows Loc or Err is the Tx or FTV family. The model number on the rating plate confirms it.
Can I keep resetting an NTI ignition lockout to get through the night?
One reset is fair. More than that pushes unburned gas through a burner that has already failed to light several times in a row, and the lockout is the control doing its job. If the house is cooling, shut off unused rooms, open cabinet doors under sinks on outside walls, and call our 24/7 line; there is no overtime surcharge.