Lochinvar Noble Error Codes: Lockouts and Fault Messages

By Ray Bennett · Updated 24 October 2026 · 10 min read · Checked against the maker’s manual

Lochinvar Noble Error Codes: Lockouts and Fault Messages

Short answer

Lochinvar Noble error codes are words on the SMART SYSTEM display, such as Flame Fail: Ignition, Air Pressure Switch or LWCO. Faults marked manual reset need the RESET button, but only once the cause is corrected. Set Point Met and Anti-Cycling need no repair, and on a Noble combi the heating waits while a hot water tap runs.

Lochinvar Noble error codes are words, not numbers: the SMART SYSTEM display on the Noble boiler and the Noble combi shows a fault message such as Flame Fail: Ignition, Air Pressure Switch or LWCO. Lochinvar marks 11 of the 30 messages in its fault table as needing a manual reset with the RESET button, once the condition has been corrected.

Two messages need no repair: Set Point Met and Anti-Cycling. Everything below comes from Lochinvar’s Noble Installation and Service Manual and its User’s Information Manual. Lochinvar says the service manual is for a qualified heating installer or service technician only, so its fixes are theirs unless this page says otherwise.

Before you start

What to carry: a torch, and the model and serial number from the boiler’s rating plate, which Lochinvar asks for when you call about the boiler.

Boiler or combi? The service manual covers the Noble boiler (NKB 80 to 199) and the Noble combi in wall mount (NKC) and floor mount (NCF) versions, 110 to 199. A combi also heats your tap water, and the messages marked Combi Only below apply to it alone.

Is it a fault? Set Point Met means the water reached the set point plus 10°F, and Lochinvar lists no action for it. Anti-Cycling means a call for heat came too soon after the last one ended; the control releases it after 60 seconds, or once the outlet temperature drops 10°F.

Radiators cold while a tap runs? On a combi that is normal. Lochinvar says the Noble does not provide heated water to the heating system during a hot water demand, so wait until the demand has ended.

Gas, overheating, flooding and freezing come first.
If you smell gas: do not try to light any appliance, do not touch any electric switch and do not use any phone in your building. Call your gas supplier at once from a nearby phone outside it and follow the gas supplier’s instructions. If you cannot reach them, call the fire department.

If it overheats or the gas will not shut off: Lochinvar says do not turn off or disconnect the electrical supply to the circulator. Shut off the gas supply at a point outside the boiler instead.

If any part has been under water: do not use it. Lochinvar says any appliance that has been under water must be replaced.

If it may be frozen: immediately shut off power and gas to the boiler and contact the factory. Lochinvar warns that running it with a frozen heat exchanger, pipes or relief valve will cause a deadly steam explosion.

Before any maintenance: disconnect the electrical supply to avoid a shock, and let the boiler cool to avoid severe burns. Lochinvar also says the installer must confirm a carbon monoxide alarm is installed in the living space before the boiler runs.

What each message means

Message	What Lochinvar says it means	RESET once fixed?
Flame Fail: Ignition	The unit failed to prove main burner ignition after several attempts	Yes
Flame Fail: Running	The unit lost its flame signal four times during a call for heat	Yes
Flame Sequence	The flame circuit sees a flame signal while the gas valve is off	Yes
Air Pressure Switch	The air pressure switch contacts are open	Yes
Fan Speed	The fan speed is outside its target	Yes
LWCO	The low water cutoff is not making	Yes
Lockout! Water Press Switch	The water pressure switch is open	Not stated
Outlet MRHL	The outlet water passed the manual reset high limit	Yes
Outlet ARHL, Outlet Temp High	The outlet water passed the automatic reset high limit, or the maximum outlet temperature	Not stated
Delta T High	The temperature rise across the heat exchanger is above the set limit	Not stated
Flue Temp Limit, Flue Temp High	The flue (stack) temperature is above its limit	Not stated
Outlet Temp DIFF	The two outlet sensors read too far apart	Yes
Flue, Outlet or Inlet Sensor Fault	A sensor is open or shorted	Yes
Lockout Inlet Sensor Fault, Outdoor Sensor Missing	The inlet sensor is disconnected or shorted; the outdoor sensor is open or shorted	Not stated
No Flue Temp Change	The flue temperature did not change after the burner started	Not stated
AUX Limit Fault	An auxiliary limit device is open	Not stated
Low Voltage	The 120 volt supply to the control dropped below 80 volts	Not stated
Memory Error	The control’s settings are corrupted	Not stated
Combi Sensor Fault (combi only)	The hot water sensor is not connected	Not stated
No Hot Water at Faucets, DHW Water is not Hot Enough (combi only)	The flow switch, the diverter valve, the set point, the mixing valve or the flow rate	Not stated

The Noble messages in four groups, from Lochinvar's Noble manuals. A: press RESET only once the cause is corrected (Fan Speed, LWCO, Flame Sequence, Air Pressure Switch, both Flame Fail messages, Outlet MRHL, Outlet Temp DIFF and the flue, outlet and inlet sensor faults). B: too hot, with technician checks (Outlet ARHL, Outlet Temp High, Delta T High, Flue Temp Limit, Flue Temp High). C: no repair needed (Set Point Met, Anti-Cycling). D: combi hot water (No Hot Water at Faucets, DHW Water is not Hot Enough).

What you can check

Check 1Free, nothing to buy

Set Point Met or Anti-Cycling: wait

Neither needs a repair. Set Point Met means the water reached the set point plus 10°F, and Lochinvar’s corrective action for it is none. Anti-Cycling holds a call for heat that came too soon after the last one; the control releases it after 60 seconds, or once the outlet temperature drops 10°F.

Check 2Free to look; a technician for the rest

Air Pressure Switch, Fan Speed or a Flame Fail: the vent and air pipes

Lochinvar’s lists for these three include a blocked vent or air intake pipe, or a blocked termination. Its user manual says the boiler shuts itself down if the air or vent is blocked. If the blockage is easy to reach and remove, remove it, and the boiler should try to restart. If the blockage is not obvious or cannot be removed, have the boiler and system checked by a qualified service technician. The same manual says the condensate line must remain unobstructed and must not be exposed to freezing temperatures.

The rest of those lists is technician work: vent lengths, wiring, the fan, the burner, the gas pressure, the gas valve and the control board. Lochinvar says to press RESET only once the condition has been corrected. Flame Fail: Ignition comes after several failed attempts; the user manual says the control makes 4 attempts before it locks out.

WHAT AN OWNER CAN LOOK AT

A B C D E

A The display and RESET press RESET only once the cause is corrected

B The pressure gauge should not read over 24 psi

C Vent and air terminations outside: must not be blocked

D Condensate trap and drain kept clear; must not freeze

E The relief valve if it often weeps, call your technician

What an owner can look at on a Noble, drawn as a plain wall hung boiler, not the real cabinet. A: the display and its RESET button, pressed only once the cause is corrected. B: the pressure and temperature gauge, which should not read over 24 psi. C: the vent and air terminations outside, which must not be blocked. D: the condensate trap and drain line, which must stay clear and must not freeze. E: the relief valve and its discharge pipe, which should not weep.

Check 3Free to look; a technician to refill or repair

LWCO or Lockout! Water Press Switch: read the gauge

LWCO means the low water cutoff is not making. Lochinvar’s first checks are the boiler pump on a call for heat, closed valves or blockages in the piping, and a system that is full of water with all the air purged. For Lockout! Water Press Switch, the first check is the water pressure at the boiler.

Look at the boiler’s pressure and temperature gauge and tell your technician what it reads. Lochinvar’s user manual says the pressure should not go over 24 psi, and higher pressure may point to the expansion tank. A relief valve that often weeps can mean the same, so call your technician.

If your system has a separate low water cutoff, testing it shuts the boiler off, and the RESET button on that cutoff turns it back on.

Check 4A technician for the water, pump or piping

Outlet MRHL, Outlet Temp High or Delta T High: the water and the pump

For these, Lochinvar’s checks start with a system that is full of water with all the air purged, boiler piping done the way its manual shows, and a boiler pump that runs on a call for heat. On a combi, it adds the diverter valve motor. Those are a technician’s checks.

If the boiler is overheating, the rule in the warning above applies: keep the circulator powered and shut the gas off outside the boiler.

Check 5Free to adjust; a technician for the parts

Combi: no hot water, or not hot enough

For DHW Water is not Hot Enough, Lochinvar’s first causes are a hot water set point that is too low, and an anti-scald mixing valve set too low. To change the set point, its user manual says: press the left button to open the SETPTS menu, press the right button to reach DHW SETPT, use the up and down buttons, then press the left button to save. Lochinvar’s service manual warns that the combi can deliver scalding water at any faucet and that a higher setting may create the potential for scald injury; to protect against it, Lochinvar requires an ASSE 1070 anti-scald mixing valve.

A third cause is too much flow, with the combi firing at 100% and still short of its set point. The service manual’s fix is to adjust a field supplied flow control valve at the mixing valve outlet, which is installer work. For No Hot Water at Faucets, Lochinvar’s first check is a hot water flow of at least 0.4 gpm; past that, it is the flow switch, the wiring and the diverter valve.

If the radiators get hot during a hot water draw and the water is not hot enough, Lochinvar points to the diverter valve not operating correctly, which is a technician’s repair.

Check 6A service call

Everything else: call a technician

Memory Error, Flame Sequence, Low Voltage, No Flue Temp Change and the sensor faults all list technician steps: wiring, sensor readings, the transformer, the gas valve or the control module. For Flame Sequence, Lochinvar’s first step is to check that no flame is present, and if one is, to turn off the gas supply and replace the gas valve.

Lochinvar says the control holds the last 10 lockouts in memory with their date and time, which helps your technician. It also says the boiler must be inspected and started by a qualified service technician at the beginning of each heating season.

What each one takes

What you see	What the work involves
Set Point Met, Anti-Cycling	Nothing; Anti-Cycling releases after 60 seconds
Air Pressure Switch, Fan Speed, Flame Fail	Clearing an easy vent or air blockage; otherwise a technician, then RESET
LWCO, Lockout! Water Press Switch	Reading the gauge; a technician to check the water and pump
Outlet MRHL, Outlet Temp High, Delta T High	A technician for the water, air, piping and pump
Not enough hot water on a combi	Raising the DHW set point; an installer for the mixing or flow valve
Sensor faults, Memory Error, Low Voltage	A technician for the wiring, sensors, transformer or control

Questions people ask

How do I reset a Lochinvar Noble boiler?

Press the RESET button on the SMART SYSTEM display. Lochinvar says the faults that need it require a manual reset once the condition has been corrected, so find and fix the cause first.

What does Flame Fail: Ignition mean on a Noble?

The boiler failed to prove main burner ignition after several attempts; the user manual says the control makes 4 attempts before it locks out. Lochinvar’s checks include the spark electrode, the gas pressure, the vent and air pipes, the gas valve and the flame sensor.

What does LWCO mean on a Lochinvar Noble?

The low water cutoff is not making. Lochinvar’s first checks are the boiler pump, closed valves or blockages in the piping, and a system full of water with the air purged. Press RESET once that is corrected.

Why is my Noble combi not heating the house while I use hot water?

Lochinvar says the Noble does not provide heated water to the heating system during a hot water demand. Once the demand has ended, Lochinvar says the combi should provide heated water to the heating system again.

What does Set Point Met mean on a Noble?

The water reached the set point plus 10°F. Lochinvar lists no corrective action for it.

The other boiler guides: boiler not working, boiler pressure, boiler keeps turning off and Lochinvar Knight boiler error codes.

Sources: Lochinvar Noble Boiler and Combi Installation and Service Manual (100275091, Rev AN; NKB 080-199, NKC 110-199, NCF 110-199) and the Noble Fire Tube Boiler and Combi User Manual (100275092, Rev M), from lochinvar.com