Boiler component graph
How InduQT connects fault codes, symptoms and data: each burner function is carried out by components, each component is watched through signals, and each fails in known ways. Every fault guide and failure signature points into this graph.
Limit and interlock supervision
Operating and safety limits, the running interlock string and low-water protection must be closed before and during firing.
| Component | Signals | How it fails | Guides |
|---|---|---|---|
| Operating and safety limits | Running interlock / limit string, Steam pressure, Boiler water temperature, Drum / water level | Operating or safety limit open, Pressure or position switch out of adjustment, Welded, jumpered or miswired contact | Feedwater and drum level instability, Fireye NX6300 F41, Fireye NX6100 F41 |
| Steam pressure / temperature sensor and control loop Also: firing-rate positioning | Steam pressure, Boiler water temperature, Firing rate | Transmitter or sensor failure, Control loop tuning or strategy, Communication wiring fault | Steam pressure drop, Fireye NX6300 F41, Fireye NX6100 F41 |
| Feedwater pump, valve and level control | Drum / water level, Feedwater flow, Steam flow | Feedwater supply shortfall, Control loop tuning or strategy, Transmitter or sensor failure, Operating or safety limit open | Feedwater and drum level instability |
Combustion air proving
The control proves combustion air is present when the fan runs, and absent when it should be off.
Ignition and pilot
Spark and pilot fuel must produce a flame the detector can prove within the pilot trial time.
| Component | Signals | How it fails | Guides |
|---|---|---|---|
| Ignition transformer and electrode | Ignition output | Igniter electrode wear or wrong gap, Ignition transformer or lead failure | Honeywell 7800 16, Honeywell 7800 28, Honeywell 7800 51, Fireye NX6300 F10, Fireye NX6100 F10 |
| Pilot gas train | Pilot valve output, Pilot gas pressure | Regulator out of adjustment or sticking, Fuel valve not opening fully, Fuel supply pressure droop | Honeywell 7800 16, Honeywell 7800 19, Honeywell 7800 28, Fireye NX6300 F10, Fireye NX6100 F10 |
Flame supervision
The flame detector and amplifier must see flame when it should exist and none when it should not.
Main fuel delivery
The fuel train must deliver stable pressure through the safety shutoff valves across the firing range.
| Component | Signals | How it fails | Guides |
|---|---|---|---|
| Main safety shutoff valves Also: valve proving and proof of closure | Main fuel valve output, Valve proof of closure | Fuel valve not opening fully, Valve seat leakage or slow closing, Welded, jumpered or miswired contact | Honeywell 7800 15, Honeywell 7800 17, Honeywell 7800 19, Honeywell 7800 33, Fireye NX6300 F11, Fireye NX6300 F42, Fireye NX6100 F11, Fireye NX6100 F42, Fireye NX6100 F30 |
| Fuel supply and regulator | Main gas pressure, Oil pressure | Fuel supply pressure droop, Regulator out of adjustment or sticking | Flame loss while firing, Steam pressure drop, Honeywell 7800 17, Honeywell 7800 19, Fireye NX6300 F10, Fireye NX6300 F42, Fireye NX6100 F10, Fireye NX6100 F42, Fireye NX6100 F43 |
Firing-rate positioning
Air damper, fuel valve and fan speed follow the commissioned fuel/air curve, proven by position switches or servo feedback.
Controller self-checks
The control checks its own relays, memory, inputs, supply and communications, and locks out if any check fails.
| Component | Signals | How it fails | Guides |
|---|---|---|---|
| Controller communication network Also: firing-rate positioning | Burner sequence state | Communication wiring fault, Electrical noise on signal wiring | Fireye NX6300 F20, Fireye NX6300 F41, Fireye NX6300 F66, Fireye NX6100 F20, Fireye NX6100 F41, Fireye NX6100 F66, Fireye NX6100 F43 |
| Burner management controller | Burner sequence state, Controller supply voltage | Controller internal fault, Supply voltage, frequency or grounding problem, Configuration or commissioning data changed, Electrical noise on signal wiring | Steam pressure drop, Honeywell 7800 13, Fireye NX6300 F15, Fireye NX6300 F64, Fireye NX6100 F15, Fireye NX6100 F64 |
Steam temperature control
On superheated-steam boilers, desuperheater spray trims main steam temperature to its setpoint as firing and load change.
| Component | Signals | How it fails | Guides |
|---|---|---|---|
| Desuperheater (spray attemperator) and its control loop | Main steam temperature, Desuperheater spray valve position, Spray water flow, Furnace temperature | Control loop tuning or strategy, Fuel valve not opening fully, Transmitter or sensor failure |
Combustion monitoring
Flue oxygen, CO and stack temperature are monitored against limits, often with trim of the fuel/air ratio.
| Component | Signals | How it fails | Guides |
|---|---|---|---|
| Flue oxygen probe and stack sensor | Flue gas oxygen, Stack (flue gas) temperature | Transmitter or sensor failure, Air/fuel ratio drift | High stack temperature |
| Boiler tubes and heating surfaces | Stack (flue gas) temperature, Flue gas oxygen, Furnace temperature, Steam pressure, Steam flow | Fouled heating surfaces | Steam pressure drop, High stack temperature |
Failure mechanisms
| Mechanism | What happens |
|---|---|
| Dirty or fogged scanner sight path | Soot, oil film, condensation or a dirty sight tube cuts the radiation reaching the detector, so the flame signal falls slowly over weeks. |
| Scanner no longer sighted on the flame root | The scanner mount, swivel or burner geometry has moved, or the flame shape changed with tuning, so the detector sees the flame only at some firing rates. |
| Detector or amplifier ageing | UV tubes and amplifiers lose sensitivity or fail on self-check with age; a UV tube can also fail "on" and see flame that is not there. |
| Flame rod or burner ground fault | A cracked insulator, a rod touching metal or poor burner grounding stops the rectified flame current from flowing correctly. |
| Electrical noise on signal wiring | Ignition or power wiring run alongside detector or low-voltage leads couples noise in, producing false flame signals or intermittent input faults. |
| Wrong detector, amplifier or configuration | The flame amplifier, detector type, response time or jumpers do not match each other or the application. |
| Igniter electrode wear or wrong gap | Eroded tips, carbon tracking, a cracked insulator or a gap outside the burner maker’s setting weakens or misplaces the spark. |
| Ignition transformer or lead failure | An open or shorted transformer winding, or a broken high-voltage lead, gives no spark or a weak one. |
| Fuel supply pressure droop | Upstream pressure sags when the valves open or other users start, starving the flame during light-off or at high fire. |
| Regulator out of adjustment or sticking | A pilot or main regulator delivers the wrong pressure, or responds slowly to the step in flow at light-off. |
| Fuel valve not opening fully | A coil, actuator or wiring fault means a safety shutoff valve opens late, partially or not at all. |
| Valve seat leakage or slow closing | A safety shutoff valve does not seal or close in time, so a leak test, proof-of-closure or pre-ignition check fails. |
| Air/fuel ratio drift | Linkage slip, a changed setpoint curve, fan wear or a fuel change moves the mixture away from the commissioned ratio, making the flame unstable or lifting. |
| Damper or valve linkage slip | A loose coupling or set screw lets the damper or fuel valve move differently from the actuator that drives it. |
| Actuator or feedback fault | A servo, feedback potentiometer or end switch no longer reports the true position, or the actuator cannot reach it. |
| Restricted combustion air path | A blocked intake, dirty fan wheel, closed inlet damper or flue restriction reduces the air pressure the fan can make. |
| Fan motor or drive fault | A tripped overload, slipping belt, failed motor or a fan VSD that is slow to reach speed delays or reduces air flow. |
| Pressure or position switch out of adjustment | The setpoint has drifted, the sensing tube is blocked or wet, or the contacts are dirty, so the switch makes or breaks at the wrong point. |
| Welded, jumpered or miswired contact | A switch or relay contact stays closed when it should be open, often from a welded contact, a jumper left in place or a wiring error. |
| Operating or safety limit open | A pressure, temperature or water-level limit opened because the process went out of range, or the limit device itself failed. |
| Transmitter or sensor failure | A transmitter, thermocouple or probe reads out of range, drifts or loses its supply. |
| Communication wiring fault | CANbus or fieldbus cabling, termination, addressing or screening problems interrupt messages between controller, display, servos and sensors. |
| Supply voltage, frequency or grounding problem | Low or noisy supply voltage, wrong phasing or a missing earth upsets the controller’s safety self-checks. |
| Fouled heating surfaces | Soot on the fire side or scale on the water side insulates the tubes, so less heat reaches the water: stack temperature and fuel use rise for the same steam output. |
| Control loop tuning or strategy | A level, pressure or firing-rate loop is too slow, too aggressive or uses too few measurements to ride through load changes. |
| Feedwater supply shortfall | The feed pump, deaerator level or feedwater valve cannot deliver the flow the boiler needs at that moment. |
| Bearing wear or misalignment | A worn, poorly lubricated or misaligned bearing raises vibration and temperature long before the machine stops. |
| Controller internal fault | A self-test, memory or safety-relay check inside the controller failed; the manufacturer usually directs replacement if it repeats. |
| Configuration or commissioning data changed | Jumpers, option parameters, a profile or a replaced servo no longer match what the controller stored at commissioning. |
The graph is InduQT’s own engineering model, written for diagnosis rather than taken from one manufacturer. Fault codes link to guides that cite the manufacturer manual. Also in knowledge.json.
Diagnose this with AI
Try Free Boiler Diagnostic Upload a photo of the alarm screen, the fault history or a data export. InduQT compares the evidence and suggests the next useful checks.