Bryant Furnace Code 33

Hi, I’m Nathan. I’ve worked as an HVAC technician for over 10 years, and Bryant furnaces are something I’ve diagnosed in basements, attics, closets, and tight utility rooms more times than I can count. If your Bryant furnace is flashing Code 33, I’ll walk you through what it actually means, what’s most likely causing it, and the safest way you can troubleshoot it yourself before you call a pro.

This guide is written the same way I’d explain it to a homeowner at the furnace, because the goal isn’t just to clear the code. The goal is to fix what caused the furnace to protect itself in the first place.

What Bryant Furnace Code 33 Means

Bryant Furnace Code 33 means a limit circuit is open. In plain English, one of the furnace safety switches that monitors overheating or unsafe flame behavior has opened the circuit to stop or limit heat.

Depending on the Bryant model, “limit circuit” can include:

• High limit switch (most common)
• Flame rollout switch (serious if tripped)
• Draft safeguard switch (on some setups)

Most of the time, Code 33 happens because the furnace is getting too hot due to restricted airflow.

What the furnace does when Code 33 happens

From what I see in the field (and how these boards are designed to respond):

• The blower usually keeps running to cool the heat exchanger.
• It may run around 4 minutes or until the switch resets, whichever is longer.
• If the switch stays open too long (commonly over 3 minutes), many Bryant boards will escalate to a lockout condition (often Code 13).

So Code 33 is basically your furnace saying:
“I’m too hot or something unsafe happened, so I’m shutting the heat down to protect the equipment and your home.”

Safety First (Read This Before You Reset Anything)

I want you to be safe and I want your furnace to stay safe.

Stop and call a professional immediately if:

• You smell gas or suspect a gas leak
• You see soot, scorch marks, or melted wires near the burners
• You see flames “rolling” or acting unusually
• The rollout switch has tripped more than once
• Your carbon monoxide alarm has gone off

If you suspect a rollout issue, do not keep resetting it to “make it run.” A rollout trip is often tied to venting or combustion problems and can become dangerous fast.

Quick Diagnosis: What Usually Causes Code 33?

In my experience, the most common cause is still the simplest: airflow.

Here’s a practical breakdown.

Common causes and fixes (fast reference)

Dirty or overly restrictive air filter	Starves airflow, heat exchanger overheats, high limit opens	Replace filter with correct size and reasonable MERV
Too many closed or blocked vents / returns	Heat can’t move, furnace temperature rises fast	Open vents, clear obstructions, check returns too
Blower problem (motor, wheel, capacitor)	Air isn’t moving enough even though burners are on	Listen, inspect, test capacitor, check wheel
Dirty blower wheel / plugged evaporator coil	Reduced airflow, overheating	Requires inspection and cleaning (often pro job)
Tripped flame rollout switch	Flame/heat detected outside burner area	Do not ignore. Investigate venting, burners, heat exchanger
Bad limit switch	Switch fails open or becomes “sticky”	Replace switch after confirming airflow is correct

Start Here: Check the Air Filter (Most Common Fix)

I know it sounds basic, but this is the #1 reason I end up clearing Code 33 quickly.

Why the filter matters so much

When a filter is clogged, your blower can’t pull enough air through the return. The heat exchanger gets hotter than it should, and the high limit switch opens to prevent damage.

What filter rating should you use?

A lot of people accidentally cause problems by installing a super high-rated filter that their system can’t breathe through.

MERV scale basics:

1–4	Basic dust	Low restriction
5–8	Better dust/pollen (common)	Moderate restriction
9–13	Allergy-focused (many homes can handle this)	Can be restrictive in some systems
14–20	Hospital-level	Often too restrictive for standard residential systems

Most residential filters fall in the MERV 1–20 scale overall, but many homes do best around MERV 8–13 depending on duct design and blower capacity.

How often should you change it?

A common baseline recommendation you’ll see referenced for typical conditions is about every 90 days. In real life, I’ve seen filters clog in 30 days with pets, renovations, or heavy run time.

What I want you to do

1. Turn the thermostat to Off
2. Locate the filter (return grille, filter rack, or near the blower compartment)
3. Pull it out and check it against a light
4. If it’s loaded with dust or you can’t see light through it, replace it

Typical filter cost: about $5–$35 depending on size and rating.

After replacing the filter, restore power and run a heat call. Many Code 33 issues end right here.

Check Supply and Return Vents (A Very Common Overheating Trigger)

If you close too many registers or block returns, the furnace can’t move enough air. The heat builds up inside the furnace, then the limit switch opens.

What I look for in a house

• Supply registers blocked by rugs, furniture, or drapes
• Return grilles blocked (returns matter just as much as supplies)
• Dampers partially closed (sometimes hidden in ductwork)
• Flex ducts pinched, crushed, or kinked

A practical rule of thumb

Try to keep most vents open. If you’re closing vents to “push air” elsewhere, it often backfires by reducing total airflow and raising furnace temperature.

Inspect the Blower System (Motor, Wheel, and Capacitor)

If your filter is clean and vents are open, the next thing I check is whether the blower is actually moving the amount of air it should.

Symptoms that point to blower trouble

Furnace lights, then shuts heat off quickly	High limit is opening from overheating
Weak airflow at registers	Blower speed issue, dirty wheel, duct restriction
Humming from blower compartment	Bad capacitor or struggling motor
Blower runs but airflow is low	Dirty wheel, slipping set screw, motor weak

What you can safely check (homeowner-friendly)

• Listen for unusual humming, grinding, or squealing
• With power OFF, remove the blower door (if accessible) and visually inspect:
  • Is the blower wheel packed with dust?
  • Is anything loose?
  • Does the wheel spin freely by hand (it should spin smoothly, not bind)

Capacitor testing (more advanced)

A weak capacitor can prevent the motor from starting properly or running at full strength.

If you have a multimeter with capacitance testing and you know how to discharge a capacitor safely, you can test it. If you don’t, this is one of those “call a tech” moments. Capacitors can bite you if handled wrong.

My field advice: If the motor is being replaced, I typically replace the capacitor as well because they wear out and can take out the new motor.

Check and Reset Rollout Switches (Only If You Know It’s Safe)

Some Bryant furnaces use rollout switches with a manual reset button (often red or white). If a rollout switch trips, it’s telling you heat or flame is where it should never be.

Where rollout switches are usually located

Near the burner area, mounted around the burner box or vestibule.

If you find a reset button

You may see a small button in the center.

If it’s tripped, it might click when pressed.

Important warning from my real-world experience

If a rollout switch trips, I don’t treat it like a nuisance reset. I treat it like a symptom.

Common underlying causes include:

• Blocked exhaust vent
• Intake/exhaust termination problems (wind issues, debris, snow)
• Burner or combustion problems
• Cracked heat exchanger (worst case)

If you reset rollout and it trips again, stop and book service.

What About a Bad Limit Switch?

Limit switches can fail, but I see airflow issues far more often than “random bad switch.”

How a limit switch fails

Over time, a limit switch can get “tired” or stick open. It’s a safety device that repeatedly opens when temperatures exceed its threshold. If the furnace has been overheating for a while (dirty filter, closed vents, weak blower), that switch gets abused.

What I do before replacing one

I confirm:

• Filter is correct and clean
• Duct and vents are open
• Blower is running properly
• Coil and blower wheel aren’t clogged

Then, if everything else checks out, replacing the limit switch becomes a logical repair.

How to Clear Bryant Code 33 (Proper Reset Process)

In many cases, Code 33 clears itself once the furnace cools and the limit circuit closes again. But you still need to address the cause.

Here’s the safe reset sequence I recommend to homeowners:

1. Set thermostat to Off
2. Turn furnace power Off at the switch or breaker
3. Wait 3–5 minutes
4. Replace filter or correct airflow issues you found
5. Restore power
6. Set thermostat to Heat and call for heat

If the code returns quickly, don’t keep cycling it repeatedly. That’s how you turn a small airflow issue into a bigger repair.

Why Code 33 Sometimes Turns into Code 13 Lockout

Many Bryant control boards will protect the furnace by escalating after a limit fault remains open too long.

• Code 33: limit circuit open
• Code 13 (common escalation): limit lockout after the fault persists (often around 3 minutes depending on model)

If you’re seeing lockout behavior, it’s another sign the furnace is repeatedly overheating or a safety circuit is not staying closed.

Prevent Code 33 From Coming Back (What I Tell Homeowners)

These are the exact habits that prevent repeat overheating calls:

Maintenance checklist

Change filter	About every 1–3 months (baseline 90 days)	Prevents airflow restriction and overheating
Keep vents and returns open	Always	Maintains designed airflow
Annual furnace tune-up	Yearly	Catches weak capacitors, dirty burners, venting issues
Keep exhaust/intake clear (high-efficiency)	Seasonal	Prevents rollout and pressure problems

When You Should Call a Technician (Even If You’re Handy)

Call a pro if:

• You replaced the filter and opened vents and Code 33 still returns
• Airflow is weak and you suspect blower or capacitor issues
• You suspect a blocked flue or intake
• A rollout switch tripped
• You see Code 33 repeatedly over multiple days

A good tech will measure temperature rise, static pressure, and verify airflow and venting. That’s how you fix Code 33 at the root instead of guessing.

Frequently Asked Questions

Final Thoughts From the Field

If there’s one thing I want you to remember, it’s this:

Bryant furnace Code 33 is usually an airflow and overheating problem, not “a random code.” Start with the filter, then vents, then the blower. If the fault persists or you find a rollout issue, it’s time to bring in a professional.