Carrier Furnace Error Codes Explained (With Fix Guide)

You walk into your basement, you spot a flashing light on the furnace, and your house is getting colder by the minute. The first instinct most people have is to start cycling the power and hope the problem disappears. 

It rarely does. 

Carrier furnace error codes are actually one of the most useful features built into your heating system, because each blinking pattern points to a specific part that needs attention. 

In this guide, our HVAC experts will walk you through what every Carrier code means, the simple checks you can do before opening the panel, the typical repair costs in Mississauga, and how to tell whether the code is a minor hiccup or a real safety issue you should not ignore.

What’s Actually Happening When Your Carrier Furnace Shows a Code

Every Carrier furnace runs through the same series of steps each time the thermostat asks for heat. When one of those steps fails, the control board picks the exact code that matches the failed step. 

So in plain terms, the code is a label that tells you where in the startup process your furnace gave up. Once you see Carrier furnace error codes through that lens, the whole system becomes a lot easier to understand.

Here is what your furnace does every single time it fires up:

1. Your thermostat calls for heat.
2. The inducer motor spins up and pulls air through the venting to create a draft.
3. Once the draft is strong enough, the pressure switch closes to confirm it.
4. Next, the hot surface igniter heats up to a glow.
5. With ignition ready, the gas valve opens, and the burners light off.
6. A steady flame is then read and confirmed by the flame sensor.
7. Warm air finally moves through the house as the blower motor kicks on a few seconds later.

A pressure switch code, like Carrier code 31, means the furnace got stuck at step three. An ignition proving failure, such as code 34, means it made it to step five but lost the flame at step six. 

The Carrier furnace blinking light on your control board is really just pointing at the exact place the sequence broke. This logic applies across the Infinity, Performance, and Comfort series because Carrier shares the same diagnostic platform across all three. 

Knowing which step failed is also why two different codes can look like the same issue from the outside, even when very different parts are involved. A weak furnace flame sensor is one of the most common reasons step six trips up in real-world Mississauga homes.

Four Things to Check Before You Open the Furnace Panel

Before you start reading code or pulling out tools, run through the four basic checks below. We get plenty of service calls in Mississauga every winter that turn out to be one of these. 

Spending five minutes here can save you a service charge and possibly a couple of cold hours in the house.

1. Look at your thermostat first. It needs to be set to Heat, and the target temperature has to be higher than the current room temperature. Many programmable thermostats also need fresh batteries every year or two. If the screen is blank, that battery is your problem.

2. Find the furnace power switch. There is a switch right on or beside your furnace that looks exactly like a regular light switch. It often gets knocked off when someone is moving storage boxes around, and that single flip stops the furnace from running. Flip it back on and give the unit a minute to wake up.

3. Check the breaker panel. The furnace runs on a dedicated 15-amp breaker, and on some installs, it shares the circuit with the air conditioner. If the breaker tripped during a summer storm, you might not notice until heating season starts. Reset it and try the unit again.

4. Pull out the air filter and hold it up to a light. When you cannot see light passing through, the filter is choked, and that alone can trigger Carrier furnace error codes like 33 or 13. A fresh filter often clears the issue on its own, especially in homes that switched to a high-MERV filter recently. 

For the right MERV rating for your specific setup, our quick guide on when to replace furnace filter walks through what works best for the GTA.

When all four checks come back clean and the Carrier furnace blinking light is still going, that is your cue to read the actual code.

How to Read the Code on Your Carrier Furnace

Carrier uses two completely different reading systems depending on your model, and this catches a lot of homeowners off guard. Figure out which group your furnace belongs to first, then follow the matching steps below.

If You Have a Performance, Comfort, or 58 Series (Flash Code)

These older and mid-range Carrier units use a yellow and a green LED on the control board. The code is a two-digit number, where the yellow flashes give you the first digit and the green flashes give you the second digit. 

Three yellow flashes followed by three green flashes means code 33, for example.

1. Find the lower access panel on the front of your furnace. There should be a small, clear window near the bottom called a sight glass.
2. Look through the sight glass, and you should see the LED behind it.
3. Count the yellow flashes during one full cycle. Then count the green flashes that follow.
4. Watch the full pattern twice to be sure your count is accurate.
5. Write the two-digit code on a piece of paper before doing anything else. 

On many Carrier models, opening the access panel cuts power to the LED through a door safety switch, and your code disappears the moment the door comes off.

If You Have a Carrier Infinity Series (Digital Code)

The Infinity series uses a communicating thermostat called the Infinity user interface, and you read the code directly from the screen rather than from a flashing light.

1. Walk up to the Infinity thermostat on your wall and open the small flip-down door at the bottom.
2. Find the Setup or Advanced option and hold it for about ten seconds until the service menu appears.
3. Scroll down to Checkout mode, which is Carrier’s name for the built-in diagnostic mode that tests every component in the system.
4. Wait for the test to finish. The screen will list each part with either a “Yes” if it is fine or an error code beside it if something failed.
5. Highlight Service Info to see any stored Carrier furnace fault codes from past failures, which gives you a history of recurring issues.

For both methods, jot the code down on paper or take a photo with your phone. If you end up calling a technician, that single number usually cuts diagnostic time roughly in half, because the tech can show up with the right parts already on the truck. 

A proper furnace service checklist always starts with reading and recording the code.

Complete Carrier Furnace Error Codes Chart

Below is the full list of Carrier furnace fault codes you might run into. The severity column tells you how urgent each one is, and we will break down the most common codes in much more detail in the next section.

Code	What It Means	Severity
11	No previous code stored	Information only
12	Blower on after power up	Information only
13	Limit circuit lockout	Serious
14	Ignition lockout	Serious
21	Gas heating lockout	Dangerous
22	Flame sensed with gas valve off	Dangerous
23	The pressure switch did not open	Annoying
24	Secondary voltage fuse blown	Serious
25	Heating with no thermostat call	Information only
31	The high-pressure switch did not close	Annoying
32	The low-pressure switch did not close	Annoying
33	Limit circuit fault (overheating)	Annoying
34	Ignition proving failure	Annoying
41	Blower motor fault	Serious
42	Inducer motor speed fault	Serious
43	Pressure switch calibration fault	Serious
44	Blower motor calibration fault	Serious
45	Control circuitry lockout	Serious
Rapid continuous flash	Reversed line voltage polarity	Dangerous

Codes 11, 12, and 25 are status codes rather than problems. The furnace is just letting you know what state it is currently in. 

So if you spot one of those without any other code beside it, your unit is fine. The codes marked Dangerous in the table need immediate shutdown, and we cover that in detail further down.

The 5 Carrier Codes You Will Probably Actually See

Out of every code in the table above, five of them account for roughly nine out of ten real service calls in our area. If you ever spot a Carrier furnace blinking light, these are the codes you are most likely staring at.

Code 33: The Furnace Got Too Hot (Most Common)

Code 33 means a safety switch opened because the heat exchanger climbed hotter than it should during operation. Your furnace shut itself off to protect the unit from damage. 

There is a Carrier-specific trap that catches plenty of GTA homeowners every year. If you switched to a high-MERV filter recently, meaning MERV 13 or higher, it can choke the airflow enough.

The fix is to drop back down to a MERV 8 or MERV 11, which still filters well without strangling the system.

What you can try yourself: Change the air filter, open every supply and return vent in the house, give the furnace fifteen minutes to cool down, then restart it. Typical Mississauga repair cost if a replacement part is needed runs $180 to $280 for a new high-limit switch.

Code 13: The Limit Lockout (Code 33’s Big Brother)

Code 13 is what happens when code 33 sticks around for more than three minutes straight. At that point, the control board decides the overheating problem is not a one-time fluke and locks the entire furnace out for safety. It will reset automatically after three hours, or you can manually cycle the power to clear it sooner.

The fixes are the same, but you are now also dealing with the lockout state on top of the original cause.

What you can try yourself: The same steps as code 33. Get the airflow sorted first, then reset the system. Repair cost matches code 33, plus any potential blower motor work if the airflow is structurally restricted by the ductwork itself.

Code 34: It Tried to Light, But the Flame Did Not Hold

Code 34 means your furnace attempted ignition, the burners actually came on for about twenty to thirty seconds. And then the flame went out before the control board could confirm it. About nine times out of ten, the flame sensor is the culprit. 

What you can try yourself: A flame sensor cleaning is the easiest real fix. Turn off the furnace power, unscrew the sensor, lightly polish the metal rod with fine sandpaper, and put it back in place. A flame sensor cleaning in Mississauga typically runs $120 to $180 if you bring in a tech, while a full replacement is closer to $180 to $260.

Code 14: The Ignition Lockout (Code 34 Three Times in a Row)

When code 34 happens three times back to back, your furnace gives up and shows code 14 instead. That is a hard lockout for three full hours. Resetting it without fixing the underlying issue does not really help, because something is clearly still stopping the flame from holding.

What you can try yourself: A flame sensor cleaning is worth attempting if you have not had one done in over a year. Mississauga repair costs for code 14 vary by what is actually wrong. Igniter replacement runs $220 to $340, while gas valve work typically falls between $350 and $600.

Code 31: The Draft Did Not Prove

Code 31 means the inducer motor started up as it should, but the pressure switch never closed to confirm that the draft is strong enough. So the furnace refuses to light the burners. This is a critical safety system. 

What you can try yourself: Step outside and check the vent termination on the exterior wall of your house. Clear any ice, snow, leaves, or other debris from around and inside the opening. 

Pressure switch replacement in our area typically runs $200 to $330, while inducer motor replacement is closer to $450 to $750. For a broader view of pricing across different types of furnace work, our breakdown of furnace repair costs in Mississauga goes much deeper.

How Much Does It Cost to Fix Each Carrier Code in Mississauga?

Repair pricing depends on the shop, parts availability, the age of your furnace, and whether the call falls inside regular business hours. The ranges below reflect typical Mississauga and GTA pricing in 2026, and they cover parts, labour, and the diagnostic visit when the repair happens during the same appointment. Emergency calls outside business hours usually run somewhat higher than these numbers.

Repair	Typical Cost (CAD)	Linked Codes
Diagnostic call only	$99 to $149	Any code
Flame sensor cleaning	$120 to $180	34, 14
Flame sensor replacement	$180 to $260	34, 14
Hot surface igniter replacement	$220 to $340	14
Pressure switch replacement	$200 to $330	23, 31, 32
High-limit switch replacement	$180 to $280	13, 33
Inducer motor replacement	$450 to $750	31, 42
ECM blower motor replacement	$650 to $1,100	41, 44
Control board replacement	$500 to $850	24, 45
Gas valve replacement	$350 to $600	21, 22
Annual tune-up (preventive)	$149 to $229	Prevents most

That annual tune-up sitting at the bottom of the list is the cheapest line item, and it is also the one that keeps you off the rest of the list. 

When you are weighing repair against replacement on an older unit, our team can help with reliable furnace repair in Mississauga and an honest assessment of whether your money is better spent fixing or upgrading.

Carrier Furnace Repair in Mississauga: How HVAC-Group Can Help

HVAC Group services Carrier furnaces across Mississauga and the wider GTA every single day. That includes the Infinity, Performance, and Comfort series from Carrier, plus the Bryant and Payne lines, since they all share the same platform and the same parts. 

Our team is fully TSSA-licensed for gas work and certified on Carrier diagnostic procedures. We stock the most common replacement parts on every service truck, so most repairs finish in one visit.

A typical Carrier repair call with our team covers the following work:

• Reading the active code on the control board or through the Infinity thermostat
• Inspecting the flame sensor, hot surface igniter, and pressure switch
• Testing gas pressure at the manifold using a calibrated manometer
• Checking inducer motor and blower motor amperage draw against spec
• Measuring temperature rise across the heat exchanger and static pressure in the ducts
• Examining the heat exchanger thoroughly for cracks or signs of failure
• Clearing the condensate trap on 95% AFUE Infinity units that handle moisture during the heating cycle
• Running a full heating cycle to verify the repair before leaving
• Clearing all stored codes from the control board once the fix is confirmed

Our coverage area includes Port Credit, Erin Mills, Meadowvale, Cooksville, Clarkson, Applewood, and every surrounding postal code in the city. 

Same-day service is available for most repair calls, and we can usually have a technician on site within a couple of hours during the heating season. 

Final Thoughts

So, you got everything you need to know about Carrier furnace error codes, from what the blinking lights actually mean down to what each repair typically costs in the GTA. 

The main idea to take away is that codes are diagnostic tools your furnace built specifically to help you, so the more comfortable you get reading them, the less stressful future breakdowns will feel. 

If you found this guide useful, please share it with anyone else in Mississauga who owns a Carrier, Bryant, or Payne furnace, because the same information applies to all three brands. 

For more home heating topics covered in the same detail, our complete furnace maintenance guide is a strong next read, and our team is always here when you need a professional eye on the system.