TL;DR
Low steam pressure with the boiler at full fire means heat transfer is degraded, most often from fireside soot or waterside scale. Compare flue gas exit temperature to baseline: a rise of more than 10 degrees C per 100 hours indicates fouling.
What you might see
- steam header pressure below operating setpoint
- boiler firing at full rate without reaching pressure
- flue gas temperature higher than baseline
- reduced steam output for the fuel consumed
Likely causes
Fireside soot deposits on the heat transfer surface reducing heat transfer to the waterside
Waterside scale from inadequate blowdown or water treatment, creating an insulating layer
Burner operating below rated fuel input from a fuel supply issue or burner fouling
Demand exceeding the boiler's rated steam capacity
Required tools
- LOTO kit
- Flue gas thermometer or thermocouple
- Tube brushing equipment (fireside)
- Fuel gas pressure gauge (for gas-fired units)
- Personal protective equipment for boiler entry: hard hat, gloves, eye protection
Safety first
- Never enter or open a boiler under steam pressure. Verify zero pressure and temperature below 50 degrees C.
- Confined space entry into a boiler requires a permit, atmospheric testing, and a standby person outside.
- Soot deposits can be spontaneously combustible when disturbed. Wet them before brushing.
Procedure
- 1
Log the current flue gas exit temperature and compare to the baseline from the last inspection. A temperature rise of 10 degrees C or more indicates fouling.[1]
- 2
Verify the burner is firing at rated fuel input. Check the fuel gas pressure at the burner train inlet (for gas) or the fuel oil flow meter (for oil). Low supply pressure reduces heat input.[1]
- 3
Lock out and cool the boiler before any internal inspection.
Warning: Never open a boiler under pressure or temperature. Confirm steam pressure is zero and temperature is below 50 degrees C before entering. - 4
Inspect the fireside heat transfer surfaces for soot deposits. Dark powdery or shiny hard deposits on the tubes indicate fouling that requires brushing or chemical cleaning.
- 5
Inspect the waterside of the tubes and shell for scale. Scale appears as a white or grey crystalline deposit. Scale thicker than 1 mm requires chemical descaling.
- 6
Record blowdown frequency and water treatment chemical feed rates. Confirm they match the boiler manufacturer's recommendation for the feedwater quality.
- 7
After cleaning, return the boiler to service and re-log flue gas exit temperature. Confirm it has returned to baseline before closing the maintenance record.
Sources
Cleaver-Brooks CB Firetube Boiler Operation, Service, and Parts Manual, Cleaver-Brooks
Cleaver-Brooks CB Boiler Operation, Maintenance and Parts Manual, fireside and waterside inspection procedures (general)
View source
More guides for Cleaver-Brooks CB / CBLE
How to reduce excessive fuel consumption on a Cleaver-Brooks CB boiler
Excess fuel use is almost always excess air in the combustion process or degraded heat transfer surfaces. Run a flue gas analysis to set the air-fuel ratio correctly, then check for scale and soot.
How to diagnose flame failure on a Cleaver-Brooks CB boiler
Most flame failure lockouts are a contaminated flame detector (UV cell or flame rod), a failed igniter, or a fuel supply problem. Clean the flame detector first. It fixes the fault in the majority of cases.
How to respond to a safety valve lifting on a Cleaver-Brooks CB boiler
A lifting safety valve means the pressure controls failed to cut the burner at the operating setpoint. Inspect the operating pressure control and high-limit control for proper setpoint and contact operation. Do not attempt to adjust or prevent the safety valve from lifting.
How to eliminate scale buildup in a Cleaver-Brooks CB boiler
Scale is calcium and magnesium carbonate or sulfate deposited from untreated or undertreated feedwater. It insulates tubes and causes overheating. Chemical descaling removes it; fixing the water treatment program prevents recurrence.
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