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Boiler signal registry

The same measurement goes by many names: stack temp, flue gas temperature, exhaust temp. The registry gives each boiler signal one name and the aliases InduQT recognises in HMI tags, historian exports and CSV column headers.

Your columnRegistry signal
TimestampNot recognised
Stack Temp (F)Stack (flue gas) temperature
O2 %Flue gas oxygen
Steam_PressSteam pressure
Firing RateFiring rate
Drum LevelDrum / water level
FW FlowFeedwater flow
Flame 1Flame signal

7 of 8 columns recognised. Unrecognised columns are still read by the AI diagnosis; the registry only helps match common names.

Worked examples: issues and the signals that reveal them

Each example shows which signals move, in what order, and what separates the issue from look-alikes. Three use simulated shapes to explain the pattern; the B-101 example is recorded plant data.

Flame loss caused by a gas pressure sag

Packaged gas-fired boiler with a flame safeguard · Illustrative example

The burner ramps toward high fire, gas pressure at the burner sags, and the flame signal collapses a few seconds later. The control locks out on flame failure, but the flame failure is the last link, not the cause.

Illustrative pattern · simulated, not plant data

Firing rateMain gas pressureFlame signalLockout
Simulated shape: gas pressure leads, flame signal follows, then the lockout.

What moves, in order

  1. Firing rate: Rises. Demand rises and the burner ramps toward high fire.
  2. Main gas pressure: Falls first. Burner gas pressure sags as flow increases: supply or regulator cannot keep up.
  3. Flame signal: Collapses. Seconds later the flame signal drops below the control’s threshold.
  4. Burner sequence state: Lockout. The control shuts the fuel valves and locks out on flame failure (for example Honeywell 7800 fault 17, Fireye F10 subset x16).

Telling it apart

  • Detection decay: flame signal drifts down over days or weeks while gas pressure stays steady.
  • Airflow problem: air pressure or the air proving switch drops out before the flame signal.
  • Ratio upset: O2 swings at the firing-rate step, but gas pressure holds.

Read more

Steam temperature dip from desuperheater spray over-correction

B-101: 130 t/h circulating fluidized-bed coal boiler (recorded incident) · Recorded data

A short combustion surge pushed main steam temperature up. The steam-temperature loop answered by opening the spray valve hard, and over-cooled the steam to 517 °C. The low-temperature alarm points at the steam side, but the cause was the control response, not a loss of firing.

Recorded plant data · Hu et al., Scientific Data 12, 742 (2025), CC BY 4.0

TE_8313B furnace760.1–797.3 °CTE_8332A main steam517.1–543.1 °CTV_8329ZC spray valve15.6–34 %YJJWSLL spray water2.7–4.1 t/hZZQBCHLL steam flow57.1–63.4 t/h517 °C
Recorded 1-minute data from B-101, 10:28 to 11:46. Each row is scaled to its own range.

What moves, in order

  1. 10:53–11:02 Furnace temperature (TE_8313B): Up. Upper furnace temperature climbs from 761 °C to 797 °C while flue gas O2 (AIR_8301A) falls to 1.15 %: a burst of extra fuel in the bed.
  2. 11:03 Main steam temperature (TE_8332A): Overshoots. Main steam temperature peaks at 543.1 °C.
  3. 11:01–11:09 Desuperheater spray valve position (TV_8329ZC): Up hard. The spray valve opens from about 16 % to 34 % and spray water (YJJWSLL) rises from 2.8 to 4.1 t/h.
  4. 11:13 Main steam temperature (TE_8332A): Dips. Main steam temperature falls to 517.1 °C, below its normal band, after the furnace temperature has already settled.
  5. 11:10–11:30 Desuperheater spray valve position (TV_8329ZC): Backs off. The valve closes back to 20–24 % and steam temperature recovers to about 534 °C.

Telling it apart

  • Not a load swing: main steam flow (ZZQBCHLL) stays between 57 and 64 t/h for the whole window, with no step before the dip.
  • Not a loss of firing: furnace temperature is back near normal when the steam temperature bottoms out.
  • The spray valve and spray flow peak just before the dip: the order of events points at the steam-temperature control loop.

Read more

Fouled heating surfaces (scale or soot)

Firetube or watertube boiler · Illustrative example

Over months, stack temperature creeps up while firing rate and flue O2 stay the same. More of the fuel’s heat leaves up the stack, so fuel use per unit of steam rises.

Illustrative pattern · simulated, not plant data

Firing rateFlue gas oxygenStack (flue gas) temperature
Simulated shape over several months: stack temperature rises while firing rate and O2 stay flat.

What moves, in order

  1. Firing rate: Steady. Pick periods at the same firing rate and steam pressure so they compare like for like.
  2. Flue gas oxygen: Steady. O2 unchanged: the air/fuel ratio has not drifted.
  3. Stack (flue gas) temperature: Creeps up. Stack temperature rises slowly over weeks or months. DOE Tip Sheet #7 recommends exactly this trend to spot scale.
  4. Steam flow: Less per unit of fuel. Steam output for the same fuel input falls as efficiency drops.

Telling it apart

  • Excess air: O2 rises together with stack temperature.
  • Step change after maintenance: stack temperature jumps at once; check baffles, turbulators and economizer bypass.
  • Higher operating pressure also raises stack temperature; confirm steam pressure is unchanged.

Read more

Fan bearing wear (FD or ID fan)

Boiler with a forced draft or induced draft fan · Illustrative example

A failing fan bearing shows up in vibration weeks before anything else. Motor current becomes noisier and creeps up late; air flow and the burner only suffer near the end, often as an airflow trip or a fan overload.

Illustrative pattern · simulated, not plant data

Fan vibrationFan motor currentCombustion air pressureOverload trip
Simulated shape over several weeks: vibration leads, current follows, air flow holds until the trip.

What moves, in order

  1. Fan vibration: Rises first. Vibration climbs over weeks, often in steps, at the same fan speed.
  2. Fan motor current: Noisier, then up. Current becomes erratic and rises as friction grows.
  3. Combustion air pressure: Holds, then drops. Air flow is normal until late; a sudden drop or an overload trip ends the run.
  4. Combustion air proving switch: Drops out late. If the fan slows or trips, the control loses air proving and locks out.

Telling it apart

  • Restricted air path: air pressure falls and current falls slightly, with no change in vibration.
  • Damper or linkage fault: air flow changes with damper position, not with time.
  • Imbalance from build-up on the wheel: vibration changes with fan speed and drops after the wheel is cleaned.

Read more

Signals

SignalTypeAlso calledUsed in
Flame signalanalog
Vdc, % or µA by controller		flame signal, flame strength, flame %, flame current, scanner signal, flm, flame1, flame 1, flame_signalFlame loss while firing, Flame scanner (UV / IR), Flame rod, Flame amplifier / flame input
Examples: Flame loss caused by a gas pressure sag
Burner sequence statestateburner status, burner state, sequence step, sequence status, ek30, bms state, burner_statusSteam pressure drop, Controller communication network, Burner management controller
Examples: Flame loss caused by a gas pressure sag
Combustion air proving switchdigitalair proving, airflow switch, air flow switch, air pressure switch, aps, caps, combustion air switchCombustion airflow faults, Combustion air proving switch
Examples: Fan bearing wear (FD or ID fan)
Combustion air pressureanalog
inWC or mbar		air pressure, combustion air pressure, windbox pressure, fan pressure, fan discharge pressureFlame loss while firing, Combustion airflow faults, Combustion air fan (FD / ID), Combustion air proving switch
Examples: Fan bearing wear (FD or ID fan)
Combustion fan runningdigitalfan run, blower run, burner motor, fan status, blower status, fan_onCombustion air fan (FD / ID)
Combustion fan speedanalog
% or Hz		fan speed, blower speed, vsd speed, fan vfd, fan hzCombustion airflow faults, Combustion air fan (FD / ID)
Main gas pressureanalog
inWC, psig or mbar		gas pressure, main gas pressure, manifold pressure, burner gas pressure, inlet gas pressure, gas_pressFlame loss while firing, Steam pressure drop, Fuel supply and regulator
Examples: Flame loss caused by a gas pressure sag
Pilot gas pressureanalog
inWC or mbar		pilot pressure, pilot gas pressure, pilot gasPilot gas train
Oil pressureanalog
psig or bar		oil pressure, fuel oil pressure, atomizing pressureFuel supply and regulator
Ignition outputdigitalignition, igniter, ignition transformer, spark, ignIgnition transformer and electrode
Pilot valve outputdigitalpilot valve, pv, pilot solenoidPilot gas train
Main fuel valve outputdigitalmain valve, mv, main fuel valve, main gas valve, sov, safety shutoff valveMain safety shutoff valves
Valve proof of closuredigitalproof of closure, poc, valve closed switch, pre-ignition interlock, pre ignition interlock, piiMain safety shutoff valves
Running interlock / limit stringdigitalrunning interlock, limit string, limits, run ilk, lockout interlock, safety limitsOperating and safety limits
Firing rateanalog
%		firing rate, modulation rate, mod rate, burner load, fire rate, output %Flame loss while firing, Combustion airflow faults, Feedwater and drum level instability, Steam pressure drop, High stack temperature, Air damper, actuator and linkage, Fuel valve actuator and linkage, Steam pressure / temperature sensor and control loop
Examples: Flame loss caused by a gas pressure sag, Fouled heating surfaces (scale or soot)
Air damper positionanalog
% or °		air damper, damper position, air servo, air actuator, air driveFlame loss while firing, Combustion airflow faults, Air damper, actuator and linkage
Fuel valve positionanalog
% or °		fuel valve position, gas valve position, fuel servo, fuel actuator, fuel drive, gas butterflyFuel valve actuator and linkage
Low fire position switchdigitallow fire switch, lfs, low fire proven, low fire startLow fire and high fire position switches
High fire (purge) position switchdigitalhigh fire switch, hfs, purge position, high fire provenLow fire and high fire position switches
Steam pressureanalog
psig or bar		steam pressure, header pressure, drum pressure, boiler pressure, steam_pressFeedwater and drum level instability, Steam pressure drop, High stack temperature, Operating and safety limits, Steam pressure / temperature sensor and control loop, Boiler tubes and heating surfaces
Boiler water temperatureanalog
°F or °C		water temperature, supply temperature, outlet temperature, hot water tempOperating and safety limits, Steam pressure / temperature sensor and control loop
Drum / water levelanalog
% or in		drum level, water level, gauge glass, lwco, low water cutoffFeedwater and drum level instability, Operating and safety limits, Feedwater pump, valve and level control
Steam flowanalog
lb/h or kg/h		steam flow, steam_flow, steam output, steam load, boiler load, steam rateFeedwater and drum level instability, Steam pressure drop, High stack temperature, Feedwater pump, valve and level control, Boiler tubes and heating surfaces
Examples: Steam temperature dip from desuperheater spray over-correction, Fouled heating surfaces (scale or soot)
Feedwater flowanalog
lb/h, kg/h or gpm		feedwater flow, feed water flow, fw flow, feedwaterFeedwater and drum level instability, Feedwater pump, valve and level control
Stack (flue gas) temperatureanalog
°F or °C		stack temperature, stack temp, flue temperature, flue gas temperature, exhaust temperature, flue tempSteam pressure drop, High stack temperature, Flue oxygen probe and stack sensor, Boiler tubes and heating surfaces
Examples: Fouled heating surfaces (scale or soot)
Flue gas oxygenanalog
% O2		o2, oxygen, flue o2, excess oxygen, stack o2Flame loss while firing, Combustion airflow faults, High stack temperature, Flue oxygen probe and stack sensor, Boiler tubes and heating surfaces
Examples: Fouled heating surfaces (scale or soot)
Fan vibrationanalog
mm/s or in/s		fan vibration, bearing vibration, vibration, fan vib, id fan vibration, fd fan vibrationCombustion air fan (FD / ID)
Examples: Fan bearing wear (FD or ID fan)
Fan motor currentanalog
A		fan current, motor current, fan amps, id fan current, fd fan current, blower ampsCombustion air fan (FD / ID)
Examples: Fan bearing wear (FD or ID fan)
Furnace temperatureanalog
°F or °C		furnace temperature, furnace temp, upper furnace temperature, bed temperature, furnace exit temperatureBoiler tubes and heating surfaces, Desuperheater (spray attemperator) and its control loop
Examples: Steam temperature dip from desuperheater spray over-correction
Main steam temperatureanalog
°F or °C		main steam temperature, steam temperature, superheated steam temperature, sh outlet temperature, steam tempDesuperheater (spray attemperator) and its control loop
Examples: Steam temperature dip from desuperheater spray over-correction
Desuperheater spray valve positionanalog
%		spray valve, desuperheater spray valve, attemperator valve, spray valve position, desuperheater valveDesuperheater (spray attemperator) and its control loop
Examples: Steam temperature dip from desuperheater spray over-correction
Spray water flowanalog
t/h or lb/h		spray water flow, spray flow, attemperator flow, desuperheater flowDesuperheater (spray attemperator) and its control loop
Examples: Steam temperature dip from desuperheater spray over-correction
Controller supply voltageanalog
Vac		line voltage, supply voltage, mains, l1, 120v, 230vBurner management controller
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