CARRIER ERROR CODE • TRI-STATE AREA
Carrier Error Code 33: Complete Troubleshooting Guide
Limit Circuit Fault - High limit or flame rollout switch is open. Learn causes, DIY fixes, and when to call a professional for this common Carrier furnace error.
What is Carrier Error Code 33?
Carrier error code 33 indicates a Limit Circuit Fault, meaning your furnace's high limit switch or flame rollout switch has opened. This is a critical safety feature designed to prevent your furnace from overheating or allowing dangerous flames to escape the combustion chamber.
When the furnace detects insufficient airflow or improper combustion, these safety switches automatically shut down the system to protect your home and equipment. The high limit switch monitors the temperature inside the heat exchanger, while the flame rollout switch detects if flames are escaping where they shouldn't be.
This error code appears on Carrier, Bryant, and Payne furnaces, which all use the same control board and diagnostic system. The LED display on your furnace will flash a pattern indicating code 33, or you may see it on a digital display depending on your model.
Safety First
Error code 33 is a safety mechanism protecting your home. While many causes can be resolved with basic troubleshooting, never ignore repeated code 33 errors. If you suspect a cracked heat exchanger or smell gas, turn off your furnace immediately and contact a professional. Carbon monoxide exposure can be deadly.
The most common trigger for error code 33 is restricted airflow caused by dirty air filters, closed supply vents, or blocked return registers. When your furnace can't circulate enough air over the heat exchanger, temperatures rise beyond safe levels, triggering the high limit switch. Understanding what causes this error is the first step to resolving it safely and permanently.
Common Causes of Carrier Error Code 33
Carrier error code 33 has multiple potential causes, ranging from simple filter issues to serious equipment problems. Here are the most common culprits, listed from most common to least common:
1Dirty or High-MERV Air Filter
The #1 cause of error code 33. A clogged filter or upgrading to a MERV 13+ filter without proper system modifications restricts airflow severely. Your furnace needs adequate air circulation to prevent overheating. Standard residential systems work best with MERV 8-11 filters. If you recently changed your filter and code 33 appeared, this is likely the cause.
2Closed or Blocked Supply Vents
Closing too many supply vents (more than 20% of total vents) creates back pressure that prevents proper airflow. Many homeowners close vents in unused rooms thinking it saves energy, but this actually forces your furnace to work harder and can trigger the high limit switch. Keep at least 80% of vents open throughout your tri-state area home.
3Blower Motor Failure or Running at Low Speed
If your blower motor isn't running at full speed or has failed completely, the furnace cannot circulate enough air over the heat exchanger. This can be caused by a faulty blower motor, bad capacitor, or incorrect speed tap settings on the control board. You may notice weak airflow from your vents even when the furnace is running.
4Faulty Blower Capacitor
The capacitor provides the electrical charge needed to start and run the blower motor. When it fails or weakens, the motor can't reach full speed, resulting in reduced airflow. Capacitors typically last 10-20 years but can fail prematurely due to heat or electrical surges. A professional can test capacitor strength with a multimeter during a maintenance visit.
5Dirty Evaporator Coil
Your air conditioning evaporator coil sits above the furnace and can accumulate dust, pet hair, and debris over time. A severely dirty coil acts like a secondary filter, blocking airflow even when your filter is clean. This is particularly common in homes with pets or poor filtration. Professional coil cleaning during annual AC maintenance prevents this issue.
6Dirty or Damaged Blower Wheel
The blower wheel (squirrel cage fan) can accumulate significant dirt and debris, especially if filters aren't changed regularly. Heavy buildup reduces airflow and makes the motor work harder. Missing or broken blower wheel blades also drastically reduce air circulation. This issue requires professional cleaning or replacement of the blower assembly.
7Flame Rollout Switch Tripped
The flame rollout switch detects when flames escape the combustion chamber—a serious safety hazard. If this switch trips, it's often due to blocked flue pipes, improper combustion air, or a cracked heat exchanger. Never ignore a tripped flame rollout switch. After resetting, observe the flame pattern when the furnace fires. Flames should be steady and blue, shooting directly into the heat exchanger tubes, not "rolling out" or appearing yellow/orange.
8Insufficient Combustion Air
80% efficiency furnaces draw combustion air from the surrounding space. If your furnace is in a tight closet or mechanical room without adequate ventilation, it can't get enough oxygen for proper combustion. 90%+ high-efficiency furnaces use PVC intake pipes to bring in outdoor air. Check that these pipes aren't blocked by snow, debris, or bird nests—especially common during winter in the tri-state area.
9Stuck High Limit Switch
Sometimes the high limit switch itself fails mechanically and stays open even when temperatures are normal. To test this, turn off power to the furnace, wait 15 minutes for it to cool completely, then check for continuity across the switch with a multimeter. If there's no continuity after cooling, the switch is faulty and needs replacement. This is less common but worth checking if all airflow issues have been ruled out.
10Cracked Heat Exchanger (CRITICAL)
This is the most serious cause of error code 33 and requires immediate professional attention. A cracked heat exchanger allows combustion gases (including carbon monoxide) to mix with your home's air supply—a life-threatening situation. Signs include repeated code 33 errors that return immediately after repair attempts, visible cracks or holes during inspection, soot buildup around the furnace, and carbon monoxide detector alarms.
⚠️ If you suspect a cracked heat exchanger, do not operate your furnace. Turn it off immediately, open windows, and contact a licensed HVAC professional for a camera inspection. Heat exchanger replacement typically requires a new furnace due to the extensive labor involved.
Pro Tip: Error code 33 often appears alongside error code 13 (Limit Circuit Lockout). Code 13 simply means the limit circuit has been open for more than 3 minutes, triggering a safety lockout. Fix the underlying code 33 issue first, and code 13 will clear automatically once the system operates properly for a full heating cycle.
DIY Troubleshooting Steps for Error Code 33
Before calling a professional, you can safely perform these troubleshooting steps. Follow them in order for the best results. If you're uncomfortable with any step, or if the problem persists, contact a licensed HVAC technician.
1Turn Off Power to the Furnace (SAFETY FIRST)
Locate your furnace's power switch (usually on or near the unit, looks like a light switch) and turn it to the OFF position. Alternatively, switch off the circuit breaker labeled "Furnace" or "HVAC" in your electrical panel. This prevents any risk of electrical shock or unexpected startup while you're working.
Why this matters: Working on electrical equipment while powered can cause serious injury or death. Always verify power is off before touching any components.
2Inspect and Replace the Air Filter
Locate your air filter (typically in the return air duct or furnace cabinet). Remove it and hold it up to a light. If you can't see light through it, or if it's visibly dirty with dust and debris, replace it immediately. If you recently upgraded to a MERV 13 or higher filter, replace it with a MERV 8-11 filter designed for residential use.
Filter replacement guidelines:
- Standard 1-inch filters: Every 30-90 days
- Homes with pets: Every 30-60 days
- High MERV filters (13+): Every 30-45 days (if your system supports them)
- 4-inch or 5-inch media filters: Every 6-12 months
Pro Tip: Write the installation date on the filter's edge with a marker. Set a phone reminder to check it monthly during heating season. A clean filter is the simplest way to prevent error code 33 and improve your indoor air quality.
3Open All Supply Vents and Return Registers
Walk through your entire home and fully open every supply vent (the vents that blow air into rooms) and return register (larger vents that pull air back to the furnace). Remove any furniture, curtains, or rugs blocking airflow. Move any items stored in front of return vents—even a couch pushed against a return can significantly reduce airflow.
Common mistake: Many homeowners close vents in unused rooms thinking it saves energy. This actually increases your energy bills and causes problems like error code 33. Modern HVAC systems are balanced to heat/cool the entire home and don't work efficiently with closed vents.
4Wait 15 Minutes for Furnace to Cool Completely
After addressing airflow issues, give your furnace at least 15 minutes to cool down completely. The high limit switch and flame rollout switches need to return to room temperature before they'll close and allow the furnace to operate. Don't rush this step—patience prevents repeated trips to the furnace.
What's happening: These safety switches are temperature-activated. They won't reset until the furnace cabinet reaches a safe temperature, typically around 110-120°F (43-49°C) or lower.
5Reset Flame Rollout Switches
Locate the flame rollout switches near the burners—they're typically small disc-shaped switches with a button in the center. Press the button firmly to reset each switch. You should hear or feel a click when it resets properly. Most furnaces have 2-3 flame rollout switches. Reset all of them.
⚠️ Warning: If a flame rollout switch won't reset or immediately trips again after resetting, this indicates a serious problem like a cracked heat exchanger or blocked flue. Do not continue troubleshooting. Call a professional immediately.
6Check Combustion Air Supply (90%+ Furnaces)
If you have a high-efficiency furnace (90% AFUE or higher), it uses white or gray PVC pipes to bring in outdoor air for combustion. Go outside and inspect both the intake (brings air in) and exhaust (releases combustion gases) pipes. Remove any snow, ice, leaves, debris, or bird nests blocking these pipes. Make sure no one has placed anything in front of them that could restrict airflow.
Winter tip: During heavy snow in the tri-state area, check these pipes daily. Snow can quickly block the intake, causing your furnace to shut down. Keep the area around the pipes clear with at least 12 inches of clearance.
7Restore Power and Test
Turn the power switch back on (or flip the circuit breaker). Set your thermostat to heat mode and raise the temperature setting above the current room temperature by at least 5 degrees. The furnace should start within 30-60 seconds. Listen for the blower motor to engage and feel the vents for warm air within 2-3 minutes.
✅ Success Indicators:
- No error codes appear on the display
- Blower motor runs continuously while heating
- Strong airflow from all supply vents
- Warm air (not hot or lukewarm) coming from vents
- Furnace runs through complete heating cycles without shutting down
8Monitor for 24 Hours
Even if the furnace starts successfully, monitor it for at least 24 hours to ensure the problem doesn't return. Error code 33 can be intermittent, especially if the root cause isn't fully resolved. Pay attention to how long heating cycles last (should be 10-15 minutes) and whether the blower motor sounds normal (smooth, not labored or grinding).
What to watch for: If error code 33 returns within 24 hours, or if you notice weak airflow, unusual noises, or short cycling (furnace turning on and off every few minutes), the problem requires professional diagnosis. Don't continue resetting the furnace repeatedly—this can cause additional damage.
Still Seeing Error Code 33?
If you've completed all these steps and error code 33 persists, or if you're uncomfortable performing any of these checks, it's time to call a professional. The issue likely involves components that require specialized tools, training, and replacement parts.
Schedule Professional DiagnosisWhen to Call a Professional for Error Code 33
While basic troubleshooting is safe for homeowners, certain situations require immediate professional attention. Don't risk your safety or cause additional damage by attempting repairs beyond your skill level.
Call Immediately If You Notice:
- Gas smell near furnace - Turn off gas supply and call your gas company and HVAC professional immediately
- Carbon monoxide alarm sounds - Evacuate home immediately, call 911, and contact HVAC professional after
- Visible flames outside combustion chamber - Indicates dangerous flame rollout; shut down furnace immediately
- Soot or scorch marks on furnace - Sign of improper combustion or heat exchanger failure
- Repeated error 33 after filter change - Indicates component failure, not simple airflow issue
Professional Service Needed For:
- Blower motor replacement - Requires electrical knowledge and proper motor sizing
- Capacitor replacement - High voltage component that can cause serious injury if mishandled
- Heat exchanger inspection - Requires camera equipment and training to identify cracks
- Limit switch replacement - Must be properly calibrated to prevent safety issues
- Blower speed adjustment - Control board programming requires technical knowledge
- Evaporator coil cleaning - Requires refrigerant handling certification in many cases
What to Expect During Professional Service
When you call Dimatic Control for error code 33 diagnosis, here's what our certified technicians will do:
Complete System Inspection
Verify error code, check all safety switches, test for continuity, and inspect visible components
Airflow Testing
Measure actual CFM (cubic feet per minute) airflow to identify restrictions and verify blower motor performance
Component Testing
Test capacitor with multimeter, check motor windings, verify switch operation, and inspect control board
Heat Exchanger Inspection
Visual inspection for cracks, camera inspection if needed, and combustion analysis to verify safe operation
Detailed Diagnosis Report
Clear explanation of the problem, repair options, and transparent information to help you make informed decisions
Professional Repair
Using quality OEM parts, proper tools, and following manufacturer specifications for lasting repairs
24/7 Emergency HVAC Service in the Tri-State Area
Don't let error code 33 leave you without heat. Our certified technicians respond fast with same-day service available.
How to Prevent Carrier Error Code 33
Prevention is always easier and less expensive than repair. Follow these best practices to minimize the risk of error code 33 and extend the life of your Carrier furnace:
Regular Filter Changes
Change your air filter every 30-90 days depending on usage, pets, and filter type. Set recurring calendar reminders. Keep spare filters on hand so you never delay a change. This single habit prevents 60-70% of error code 33 occurrences.
Annual Professional Maintenance
Schedule professional furnace maintenance every fall before heating season. Technicians clean components, test safety systems, verify airflow, and catch small issues before they become major repairs. Our maintenance plans include priority service.
Keep All Vents Open
Never close more than 20% of supply vents. Keep furniture away from vents and returns. Ensure nothing blocks airflow—even decorative vent covers can restrict airflow if not designed properly. Your system works best heating the entire space it was designed for.
Use Correct MERV Rating
Stick to MERV 8-11 filters unless your system is specifically designed for higher filtration. If you need better air quality, consider a whole-home air purifier instead of over-filtering your furnace, which causes strain and triggers error codes.
Clear Outdoor Combustion Pipes
For high-efficiency furnaces, check PVC intake and exhaust pipes monthly during winter. After heavy snow or storms in the tri-state area, inspect immediately. Keep the area around these pipes clear with at least 12 inches of clearance on all sides.
Address Issues Immediately
Don't ignore early warning signs like weak airflow, unusual noises, short cycling, or intermittent error codes. Small problems quickly become expensive repairs. Contact a professional at the first sign of trouble—it's always cheaper to fix issues early.
Join Our Maintenance Plan
Dimatic Control offers comprehensive HVAC maintenance plans that include annual tune-ups, priority service scheduling, discounts on repairs, and extended warranties. Our maintenance customers experience 80% fewer emergency breakdowns and save an average of 15% on energy bills.
Learn More About Maintenance PlansRelated Carrier Error Codes
Error code 33 often appears alongside other Carrier furnace codes. Understanding these related codes helps you diagnose the complete picture:
Error Code 13: Limit Circuit Lockout
Appears when the limit circuit has been open for more than 3 minutes. This is the safety lockout that follows repeated code 33 errors. Fix the underlying code 33 issue first.
Learn MoreError Code 14: Ignition Lockout
The furnace failed to ignite after multiple attempts and locked out for safety. Can be caused by gas supply issues, dirty flame sensor, or failed igniter.
Learn MoreError Code 31: Pressure Switch Fault
The pressure switch didn't close or opened unexpectedly. Common causes include blocked venting, failed inducer motor, or stuck pressure switch.
Learn MoreError Code 34: Ignition Proving Failure
The flame sensor doesn't detect flame after ignition. Usually caused by dirty flame sensor, improper flame sensor position, or gas pressure issues.
Learn MoreNeed help with a different error code? Browse our complete HVAC error code library covering Carrier, Lennox, Trane, Rheem, and York systems. Each guide includes detailed troubleshooting steps, professional repair information, and prevention tips.
Frequently Asked Questions About Carrier Error Code 33
What is Carrier error code 33?
Carrier error code 33 is a Limit Circuit Fault, meaning the high limit or flame rollout switch is open. This safety mechanism prevents furnace overheating and typically indicates an airflow problem caused by restricted airflow, dirty filters, or blocked vents.
Can I fix Carrier error code 33 myself?
You can perform basic troubleshooting like changing the air filter, opening all vents, and resetting flame rollout switches. However, if the issue persists or involves the heat exchanger, call a professional immediately due to carbon monoxide risks.
Is Carrier error code 33 dangerous?
Error code 33 itself is a safety mechanism protecting your home. However, if caused by a cracked heat exchanger, it presents a serious carbon monoxide hazard. Never ignore repeated code 33 errors - contact a licensed HVAC professional.
Why does Carrier error code 33 appear after changing the air filter?
High MERV-rated filters (MERV 13+) restrict airflow more than standard filters. If you upgraded to a higher MERV filter, the furnace may not get enough air, triggering the high limit switch. Use MERV 8-11 for most residential furnaces unless your system is specifically designed for higher filtration.
How do I reset Carrier error code 33?
Turn off power to the furnace, wait 15 minutes for it to cool, then reset the flame rollout switches by pressing the button behind the disc. Address the underlying cause (dirty filter, blocked vents, etc.) before restarting to prevent the code from returning.
What's the difference between Carrier error code 33 and 13?
Error 33 is a Limit Circuit Fault (limit/rollout switch open). Error 13 is Limit Circuit Lockout (switch has been open for 3+ minutes). Code 13 is a safety lockout that requires addressing code 33's root cause first before the system will operate again.
Can a dirty air filter cause Carrier error code 33?
Yes, a dirty air filter is one of the most common causes of error code 33. Restricted airflow from a clogged filter prevents proper heat exchange, causing the high limit switch to trip as a safety measure to prevent overheating.
How often should I change my Carrier furnace filter to prevent code 33?
Change standard 1-inch filters every 30-90 days depending on usage, pets, and allergies. Higher MERV filters may need more frequent changes (30-60 days). Check monthly during heating season and replace when visibly dirty.
What MERV rating should I use to avoid Carrier error code 33?
Most residential Carrier furnaces work best with MERV 8-11 filters. MERV 13+ filters improve air quality but can restrict airflow and trigger code 33 if your system isn't designed for high-efficiency filtration. Check your furnace manual for recommended filter specifications.
Can closed vents cause Carrier error code 33?
Yes, closing too many supply vents or blocking return registers restricts airflow, causing the furnace to overheat and trip the high limit switch (code 33). Keep at least 80% of vents open for proper system operation.
What is a flame rollout switch and why does it cause code 33?
The flame rollout switch is a safety device that detects flames escaping the combustion chamber. If triggered, it opens the circuit (code 33) to prevent fire hazards. Causes include cracked heat exchangers, blocked flues, or improper combustion air.
How do I know if my heat exchanger is cracked (code 33)?
Signs include repeated code 33 errors, flame rollout switch tripping, visible cracks during inspection, soot buildup, and carbon monoxide detector alarms. A professional with a camera inspection can confirm. Never operate a furnace with a suspected cracked heat exchanger.
Who can fix Carrier error code 33 in the tri-state area?
Dimatic Control LLC provides expert Carrier furnace repair in the tri-state area. Our certified technicians offer 24/7 emergency service and same-day appointments. Call (908) 356-HVAC for immediate assistance with error code 33.
How long does it take to fix Carrier error code 33?
Simple fixes (filter change, reset switches) take 15-30 minutes. Component replacement (capacitor, motor) takes 1-2 hours. Heat exchanger replacement requires 4-8 hours. Diagnosis typically takes 30-60 minutes with our professional technicians.
Can I prevent Carrier error code 33 from happening again?
Yes! Regular maintenance prevents code 33: change filters every 30-90 days, schedule annual professional tune-ups, keep vents open and unobstructed, use the correct MERV rating for your system, and address any airflow issues immediately when they arise.
Expert Carrier Furnace Repair in the Tri-State Area
Dimatic Control LLC has been serving homeowners across the tri-state area since 2013. Our certified technicians diagnose and repair Carrier error code 33 quickly and correctly the first time.
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