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MEDIUM URGENCY

Carrier Code 33 — Limit or Flame Rollout Switch Open

Code 33 (3 short + 3 long flashes)

Limit or flame rollout switch open — usually restricted airflow.

Brand: Carrier (Also covers Bryant, Payne)  |  Equipment: Gas Furnace

SAFETY: If the rollout switch (not the limit switch) is what tripped, flames are escaping the burner enclosure. This is a CO hazard. If the code returns after clearing the filter, shut off gas and call a licensed HVAC tech.

What This Code Means

Code 33 flashes as 3 short pulses followed by 3 long pulses. It means a safety switch — the high-temperature limit switch on the heat exchanger or the flame rollout switch near the burners — has tripped open due to overheating or combustion issues.

Likely Causes (Ranked)

Most common (~60%)

Dirty air filter

What: Restricted airflow causes heat to build up in the heat exchanger; limit switch trips.

How to check: Hold filter to a light — should pass light easily.

Fix: Replace filter; cycle power.

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Common

Closed registers or blocked returns

What: Excess static pressure from too many closed vents triggers the switch.

How to check: Walk through house and open all vents.

Fix: Open vents, clear returns, wait 15 minutes.

Common

Failed blower motor

What: Slow or seized blower can't remove heat from exchanger fast enough.

How to check: Listen for blower during heat cycle; should run smoothly.

Fix: Test capacitor first; replace motor if failed.

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Less common but serious

Flame rollout (heat exchanger crack)

What: Flames escape the burner box — possibly cracked heat exchanger.

How to check: Check rollout switch button — if popped, this is the cause.

Fix: Stop using furnace; call HVAC tech — CO risk.

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Diagnostic Steps

  1. Cut power 60s
  2. Replace dirty air filter
  3. Open all supply registers and clear returns
  4. Restart and watch for code return
  5. If rollout switch tripped, stop and call pro

Frequently Asked Questions

Can I reset Carrier code 33 myself?
For one-time filter trips, yes. If it returns within 1-2 cycles, don't keep resetting — there's an underlying problem.
Is Carrier code 33 dangerous?
The limit switch is doing its job. But if a rollout switch is the source, there may be a cracked heat exchanger and CO release. Get an inspection.
How much to fix Carrier code 33?
Filter: under $20. Blower motor: $200-500. Heat exchanger: often $1500-3000 or furnace replacement.
Same code on Bryant or Payne?
Yes — all three brands share the same control board and code system.

Related Carrier Codes

Carrier Error Code 31Carrier Error Code 14

Related Symptoms

Furnace Keeps Shutting OffFurnace Short CyclingFurnace Blowing Cold Air

Need More Help?

Try our interactive symptom diagnostic tool or browse Carrier parts.

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