Working in the field with Continuous Emissions Monitoring Systems (CEMS), you’ve probably dealt with your fair share of headaches — filters clogged solid, water where it doesn’t belong, erratic analyzer readings, and equipment that just won’t behave.
These CEM system failures don’t just cause frustration — they can lead to compliance issues, lost data, and costly downtime.
We’ve pulled together some of the most common CEMS maintenance problems we’ve seen on the job — and how to fix or avoid them entirely.
1. Plugged Probe Filter
A clogged probe filter, overwhelmed by glass particulate from the furnace.
- Excessive suction pulling in particulate = Eductor pressure may be too high
- Incorrect probe type for plant’s application (Example: SP2000 instead of SP2006)
- No impingement shield
- The furnace process generates excess dust
- Reduce suction at the probe by lowering the eductor pressure.
- Modify the furnace process to reduce particulate generation—this may require better filtration or adjusting the exhaust temperature. Recommend a switch to a dilution probe.
- Install a probe impingement shield on the stinger to limit debris entering the probe cavity.
Selecting the right probe type and optimizing process parameters can significantly reduce particulate load and extend component life.
Example: The type of probe installed at this plant — an M&C SP2000 — wasn’t the best fit for the application. Due to the high particulate levels in the furnace exhaust, an M&C SP2006 dilution probe was recommended and installed. The dilution probe is better suited for this environment because it allows for special filtering techniques and uses materials that handle harsh, particulate-heavy conditions more effectively. ESC Spectrum’s field service team identified the mismatch and guided the upgrade.
2. Water Slip (Too Much Moisture Reaching Analyzers)
One of the most common CEMS issues we encounter is water making it past the chiller. This “water slip” problem can damage analyzers and lead to erratic calibration.
Water slip due to inadequate chiller capacity and high sample flow.
- The flow rate is too high
- The chiller temperature is too warm
- Ineffective heat exchanger
- Moisture carried through to ammonia filters
- Reduce the flow rate
- Reduce chiller temperature from 5.5°C to 4°C
In the video, the sample conditioner had too much flow, and the chiller (heat exchanger) wasn’t sized properly for the volume moving through it. Because the flow was too fast, the heat exchanger couldn’t remove all the moisture. On top of that, the chiller temperature was set too warm, making it even harder to remove the remaining water from the sample. This combination of high flow and insufficient cooling allowed moisture to slip past the sample conditioning system and collect in the ammonia filters — a problem we refer to as “Water Slip.”
3. Dirty Instrument Air System
Dirty, wet, or oily air reaching CEMS components due to neglected air cleanup systems.
Poor air dryer maintenance
Why It Matters:
These systems filter plant air to provide clean, dry air to analyzers and other sensitive components.
- Regularly replace desiccant and filters
- Inspect tubing for moisture or oil
- Include air cleanup systems in routine PM schedules
4. Corroded Components (aka "Green Slime")
Corroded instrumentation from acidic condensate and contamination.
Incompatible tubing and components exposed to harsh conditions.
- Use corrosion-resistant tubing
- Routinely flush and inspect lines
5. Improper Shelter HVAC
Small AC unit used instead of a full HVAC
No heater = unstable temps leading to analyzer drift and calibration headaches
- Install proper HVAC system
- Maintain 72–75°F inside shelter
6. Dirty Gas Cooler
A gas cooler hadn’t been cleaned in years — corrosion and dirt buildup were rampant.
Immediate cleaning and inspection
Added quarterly visual inspections to PM routine
Good housekeeping extends the life of your system. Don’t wait for failure to clean.
7. Melted Umbilicals
Umbilicals melted due to water ingress and insulation breakdown.
Poor bundling and lack of moisture control
- Replace bundle
- Use heated, insulated umbilicals
- Inspect for leaks before cold weather hits
- Seal connections
- Moisture-proof entry points
8. Probe Tubes and Sample Ports Neglected
Clogged, broken, or corroded ports that caused complete data loss.
Little to no preventative maintenance
- Inspect every 12–24 months
- Replace components showing wear or buildup
9. Winter Sample System Failures
Cold-weather failures including flange leaks, clogged tubes, and erratic calibration drift.
Keep components above 350°F
Maintain consistent temperature with proper insulation
10. Misaligned Flange Bolt Patterns
Crooked installation due to incorrect flange bolt patterns.
- Double-check pattern before install
- Use a flange drawing
- Use a standard QA checklist
11. Disorganized CEMS Racks
Disorganized, unrecognizable equipment setup with poor maintenance.
- Full system inspection
- Reorganize and label components
For more detailed advice on keeping your CEMS equipment in top shape, read our guide on hardware maintenance, system upgrades, and spare parts management. Field Service Tech V and Subject Matter Expert John Cutaia shares practical tips to help you reduce downtime and extend the life of your CEMS: Minimizing CEMS Downtime: Maintenance & Upgrade Strategies
Final Takeaway
Most CEMS system failures aren’t flukes — they’re the result of skipped maintenance, bad fit equipment, or environmental factors like temperature and moisture. But the good news? Most of them are preventable.
If you’re experiencing frequent CEMS analyzer drift, sample system clogs, or temperature control problems, our team is here to help with field-proven solutions. Contact ESC Spectrum — our experts have been there, fixed that.
Want to learn more about CEM systems and maintenance? Enroll in our online CEMS training courses.
Taylor Hempel - Marketing Specialist II
Taylor Hempel is a skilled marketer specializing in content creation, social media management, and driving customer engagement. With a BBA in Marketing from the University of Texas at San Antonio, she joined ESC Spectrum in February 2022. Taylor is adept at crafting informative content about continuous emissions monitoring systems, its components and data acquisition systems allowing her to craft content that educates and informs industry professionals.
Contact Taylor at thempel@escspectrum.com for questions or comments.
