Field Reference / Performance / Troubleshooting Guide
Module 05
Module 05 · Performance

Troubleshooting Guide

Symptom-led reference for diagnosing common fired heater problems. Start with what you can observe — instrument readings, flame appearance, stack colour — then follow the probable causes and actions. Filter by system or search by keyword.

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How to use this guide
Find the symptom that matches what you are seeing. Each card lists probable causes (most likely first), checks to confirm, and corrective actions. Urgency bands: Immediate = act now / consider ESD; Prompt = resolve this shift; Monitor = track trend, schedule correction.
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Black or dense smoke from stack
Combustion Prompt
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Probable causes
  • Insufficient combustion air — air registers closed too far or damper restricting flow
  • Stack O₂ below 1% — fuel-rich across all burners
  • Burner tips partially blocked — poor atomisation
  • Fuel gas liquid carryover — condensate entering burner
  • Tube failure — process hydrocarbons burning in firebox
Checks to confirm
  • Read stack O₂ — below 1% confirms rich combustion
  • Check air register position at each burner front
  • Check stack damper position — confirm open
  • Inspect flame colour via peephole: lazy orange-yellow flame confirms rich condition
  • Check fuel gas KO drum level — liquid carryover?
  • Check all pass outlet temperatures — sudden drop on one pass suggests tube leak
Corrective actions
  • Open air registers incrementally — allow O₂ to respond before further adjustment
  • Open stack damper if accessible
  • Drain fuel gas KO drum if liquid level present
  • If tube leak suspected: do not adjust combustion air — initiate controlled shutdown
  • If black smoke persists with O₂ > 2%: inspect burner tips at next opportunity
See also Upset Recognition · Tube Failure / Leak
Flame lifting or instability at burner tips
Combustion Prompt
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Probable causes
  • Excess combustion air — too much velocity through tip, flame root blows off
  • Low fuel gas pressure — insufficient momentum at tip
  • Wrong tip size — oversized for current fuel throughput
  • High draft pulling air through tip too fast
  • Fuel composition change — calorific value drop
Checks to confirm
  • Stack O₂ > 5–6% — confirms excess air
  • Observe flame at peephole: flame roots intermittently lose contact with tip
  • Check fuel header pressure trend — falling trend?
  • Check draft reading — excessive draft worsens lifting
  • Review any recent fuel system changes or feed composition shift
Corrective actions
  • Close air registers slightly — reduce excess air
  • Partially close stack damper if draft excessive
  • Check fuel header pressure — restore if low
  • If instability is severe or flame roots repeatedly lift: shut that burner on normal flameout procedure
  • Do not continue operation with a burner at risk of intermittent flameout
See also Flame-out Response · Burner Types & Operation
Flame impingement on process tubes
Combustion Immediate
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Probable causes
  • Burner tip misaligned — tip orientation directing flame toward tube
  • Over-firing at one or more burners
  • Air register closed too far — long, rich, luminous flame extends to tube
  • Tip damaged or partially blocked — asymmetric flame pattern
  • Wrong tip type for service
Checks to confirm
  • Peephole observation: flame visibly touching tube surface
  • TMT (tube metal temperature) elevated on affected row
  • Localised glowing or discolouration visible on tube
  • Check which specific burner is the origin of the flame
  • IR gun / pyrometer measurement on suspect tube during field round
Corrective actions
  • Reduce firing on that burner immediately
  • Open air register to shorten flame length
  • Do not restore full firing until cause is corrected
  • If TMT continues rising: reduce overall heater duty
  • Schedule burner tip inspection and realignment at first opportunity
  • Notify process engineer — document TMT exceedance
Escalate if TMT reaches or exceeds design limit. Continued operation risks creep damage and tube failure. → Tube Failure protocol
Coil outlet temperature (COT) rising unexpectedly
Process / Flow Immediate
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Probable causes
  • Reduced process flow — pump issue, valve position, blocked strainer
  • Coking in tubes — flow restriction, poor heat transfer to fluid
  • Firing rate higher than intended — fuel control valve issue
  • Feed composition change — higher specific heat requirement
  • TE (temperature element) calibration drift — apparent reading only
Checks to confirm
  • Check process flow against setpoint — confirm actual flow, not just controller output
  • Cross-check COT against other pass outlet temps — one pass high = localised issue
  • Check fuel gas flow rate and firing rate trend — is it actually higher?
  • Compare TMT to COT — diverging TMT vs COT indicates coke buildup
  • Check TE against adjacent redundant sensor if available
Corrective actions
  • Reduce firing rate immediately while investigating
  • Restore process flow if reduced — identify and fix cause
  • If coking suspected: notify process engineer; reduce throughput; plan decoking
  • If firing rate is the cause: check fuel control valve and trim manually
  • Do not allow COT to reach design limit — initiate controlled shutdown if trend continues
Escalate if COT within 10°C of design limit and trend not arrested within 5 minutes of firing reduction. → ESD procedure
Pass outlet temperatures diverging — one pass significantly hotter
Process / Flow Prompt
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Probable causes
  • Partial coking in one pass — increased resistance reduces flow
  • Pass flow control valve or restriction orifice fault
  • Localised flame impingement on that pass
  • Fouling at inlet distributor
Checks to confirm
  • Compare all pass outlet temperatures — which passes are affected?
  • Check pass flow indicators — is the hot pass running low flow?
  • Review TMT trend on hot pass tubes — rising faster than others?
  • If available: differential pressure across each pass coil
  • Peephole observation — any burners firing preferentially toward that side?
Corrective actions
  • Re-balance pass flows using manual valves — increase flow to hot pass
  • Reduce overall firing to protect hot pass while balancing
  • If coking suspected: plan decoking; monitor rate of divergence
  • Notify process engineer — throughput reduction may be needed
  • Document trend — rate of divergence determines urgency of decoking
See also Online / Offline Decoking
Firebox pressure at zero or positive — blowback risk
Draft Immediate
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Probable causes
  • Stack damper closed unexpectedly — actuator failure, auto-control issue
  • Convection section soot plugging — restriction to flue gas flow
  • ID fan trip (on fan-draft heaters)
  • Very sudden increase in firing rate
  • Cold stack — draft not yet established on startup
Checks to confirm
  • Read local draft gauge — confirm positive or zero reading
  • Check stack damper position — is it open?
  • Check ID fan status (if applicable)
  • Look for flames or hot gas at any heater opening — do not approach peepholes head-on
  • Check convection section differential pressure if available
Corrective actions
  • Reduce firing rate immediately
  • Open stack damper if accessible and safe to do so
  • Restore ID fan if tripped — investigate trip cause before restart
  • If firebox remains positive and cannot be corrected: initiate controlled shutdown
  • Do not open inspection doors or approach peepholes while positive
Danger Never approach any firebox opening while pressure is positive or unknown. Hot gas and flame will eject. Confirm negative draft at local gauge before any approach. → ESD if uncontrolled
Excessive draft — O₂ above target, efficiency loss
Draft Monitor
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Probable causes
  • Cold ambient conditions — increased stack buoyancy
  • Stack damper more open than needed
  • Low firing rate — less flue gas but damper position unchanged
  • Damper stuck open — mechanical fault
  • Air infiltration through casing, doors, or damaged seals
Checks to confirm
  • Stack O₂ above 5–6% (target typically 2–4%)
  • Flue gas exit temperature lower than normal — excess cold air diluting
  • Flame appearance: short, hard, blue-white — very lean
  • Check damper position indicator — is it fully open?
  • Inspect casing for visible air ingress gaps
Corrective actions
  • Close stack damper partially — observe O₂ response before further adjustment
  • If auto draft control fitted: lower setpoint slightly
  • Close individual burner air registers as secondary measure
  • Inspect and seal any casing air infiltration points
  • If damper mechanically stuck: operate at elevated excess air; schedule repair
See also Draft & Airflow Control · Thermal Efficiency
Fuel gas header pressure fluctuating
Mechanical Prompt
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Probable causes
  • Fuel gas KO drum high level — condensate carryover reaching burners
  • Refinery fuel gas system pressure fluctuation — load changes elsewhere
  • Fuel pressure control valve hunting or instability
  • Partial blockage in fuel supply line or filter
  • Fuel gas composition change — calorific value varying
Checks to confirm
  • Check fuel gas KO drum level — drain if elevated
  • Check fuel pressure trend — is it cyclic or random?
  • Check fuel pressure control valve output vs actual pressure — valve hunting?
  • Check refinery fuel gas header pressure — is this system-wide?
  • Observe burner flames — pulsing or surging confirms pressure variation reaching burners
Corrective actions
  • Drain KO drum immediately if level is high
  • If pressure control valve is hunting: switch to manual control temporarily
  • Notify instrument technician if valve requires tuning
  • If refinery header pressure is the cause: notify shift supervisor — may need to reduce firing
  • If condensate carryover causes multiple flameouts: initiate controlled shutdown
Risk Liquid condensate at burner tips causes sudden flameout. Multiple simultaneous flameouts with fuel still flowing is a pre-explosion condition. → Flame-out Response
Stack / flue gas exit temperature higher than normal
Efficiency Monitor
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Probable causes
  • Convection section fouled with soot — reduced heat transfer
  • Excess combustion air — additional mass flow carrying heat out of stack
  • High firing rate — more heat generated than convection section can absorb
  • Convection tube external fouling or internal scaling
  • Air preheater (APH) fouling if fitted
Checks to confirm
  • Check stack O₂ — high O₂ alongside high stack temp = excess air issue
  • Review stack temp trend — sudden rise vs gradual rise indicates different causes
  • Check convection section differential pressure — elevated dP confirms soot fouling
  • Compare current efficiency (fuel/duty ratio) against baseline
Corrective actions
  • If excess air: close damper / air registers to reduce O₂ to 2–4%
  • If soot fouling: schedule sootblowing or convection section cleaning
  • If convection tubes fouled internally: plan for inspection and cleaning at next shutdown
  • Log and trend — report to process engineer if efficiency deterioration is significant
Note A 20°C rise in stack temperature above baseline represents approximately 1% efficiency loss. Trend over weeks/months to quantify cost of deferred cleaning.
Unexpected ESD trip — cause unknown
Safety Systems Prompt
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Common trip initiators
  • Low process flow — FT impulse line blocked; pump trip; control valve issue
  • High COT — actual loss of flow; coking; TE calibration drift
  • Flame failure — flame detector lens fouled; fuel pressure fluctuation
  • High firebox pressure — damper fault; soot bridge; rain ingress to stack
  • Manual ESD — operator-initiated; tube failure; external fire
Investigation sequence
  • Read BMS trip log — identify the first-out trip initiator
  • For low flow: check FT against independent indicator; verify pump and valve status
  • For high COT: cross-check adjacent TEs; review flow trend
  • For flame failure: check other burner FD status; check flame detector lens condition
  • For firebox pressure: check damper position; check convection dP
  • Do not assume instrument fault without positive evidence
Before restart
  • Identify and confirm root cause — do not restart on assumption
  • Complete full BMS reset and purge sequence
  • Confirm all restart permissives satisfied
  • Notify process engineer and shift supervisor — document cause
  • If cause is instrument fault: confirm independently before startup; tag for maintenance
See also Emergency Shutdown · Burner Management System · Startup Procedure
BMS flame detector showing flame failure while burner appears lit
Safety Systems Prompt
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Probable causes
  • Detector lens fouled — soot or condensation blocking UV/IR sensor
  • Detector cooling air failure — overheating sensor
  • Detector body or conduit damaged
  • Wiring fault — intermittent signal loss
  • Flame genuinely intermittent — check before assuming instrument fault
Checks to confirm
  • Visually confirm flame is present via peephole — approach from side, confirm negative draft first
  • Check detector cooling air supply is flowing
  • Check detector signal on BMS — constant fail or intermittent?
  • Check adjacent burner detectors — are others stable?
  • If flame is intermittently present: treat as a real flame instability issue, not instrument
Corrective actions
  • Clean detector lens if accessible (follow site permit procedure)
  • Restore cooling air supply if failed
  • Notify instrument technician — do not bypass BMS protection without authority
  • If BMS trips the burner on false signal: follow normal flameout re-ignition procedure
  • Document fault — recurrent false trips on same detector require maintenance investigation
Note Confirm flame is genuinely present before categorising any detector signal as a fault. A BMS trip on a real flameout is the system working correctly.
No matching symptoms found. Try different keywords.

Quick-reference: symptom → first action

When something is wrong and there is no time to read in depth — use the table below for the immediate first action, then refer to the full card above.

Immediate First Actions by Symptom
Symptom First action Escalate to
Black smoke from stack Open air registers; check O₂ Tube failure check if O₂ already adequate
Flame impingement on tube Reduce firing on that burner immediately Tube failure protocol if TMT at limit
COT rising unexpectedly Reduce firing rate; confirm process flow ESD if COT within 10°C of design limit
Firebox pressure positive Reduce firing; open stack damper; do not approach openings Controlled shutdown if not corrected
Fuel gas pressure fluctuating Drain KO drum; check for condensate carryover Controlled shutdown if multiple flameouts
Unexpected ESD trip Read BMS first-out log; do not assume instrument Process engineer before restart
Pass temp divergence Re-balance pass flows; reduce overall firing Decoking plan if coking confirmed
Flame lifting / instability Close air registers; check fuel pressure Shut burner if instability persists
← Performance Monitoring Inspection Checkpoints →