Carrier status code 13: the lockout that follows a limit or rollout switch
Carrier status code 13 is a limit or flame rollout switch lockout on two-stage furnace controls. Learn what it records and why it outranks a reset.
What this means
Carrier lists status code 13 as a limit or flame rollout switch lockout. The control had already seen that circuit open, reported it, and then decided the condition had lasted long enough to stop trying. A lockout is a deliberate refusal to restart, so code 13 is a stronger statement than the open-circuit code that precedes it.
Equipment and model context
Carrier deluxe two-stage gas-fired induced-combustion furnaces with PSC or ICM blower motors, as covered by troubleshooting guide 58-3T
- Deluxe two-stage induced-combustion furnaces with PSC blower
- Deluxe two-stage induced-combustion furnaces with ICM blower
This reading is taken from Carrier troubleshooting guide 58-3T, which covers deluxe two-stage gas-fired induced-combustion furnaces with PSC or ICM blower motors. Other Carrier furnace controls, and the same numbers on Bryant or Payne equipment, are read from their own literature. Confirm the model on the furnace rating plate first.
What you may notice
- The furnace produces no heat and the diagnostic LED repeats one flash followed by three flashes behind the sight glass.
- Heating had been cutting out part way through cycles for some time before the lockout appeared.
- The furnace stays locked out for an extended period and then attempts to run again without anyone touching it.
Likely causes
- A high-limit switch opens when the temperature in the furnace air path exceeds its rating, which restricted airflow can produce.
- A flame rollout switch opens when heat is present where the burner compartment safety is positioned to detect it.
- An open conductor or a poor terminal anywhere in the series safety circuit presents the same electrical picture as an opened switch.
Diagnostic paths
Heat had been dropping out before the lockout
For days or weeks, heating cycles ended early with the blower continuing, and only later did the furnace stop responding to the thermostat altogether.
Change the filter if it is loaded and confirm supply registers and return grilles are unobstructed, then leave the furnace off and report the earlier pattern to service.
There is soot, scorching, or a smell near the burner compartment
Discoloration, soot marks, an unusual odour, or visible heat outside the normal burner path appears around the furnace cabinet.
Turn the heating system off at the switch beside the furnace and keep it off until a licensed gas engineer has looked at it. A manual reset button on a rollout device is not yours to press.
The furnace restarts itself hours later
Nobody intervened, yet the furnace attempted a heating cycle again after a long pause, and the lockout may then return.
Record when it locked out and when it retried. An automatic retry after a fixed interval is designed behaviour and does not mean the condition cleared.
Escalation is the point of this pair of codes. An opened safety circuit is reported first, the control waits, and if nothing changes it stops offering heat rather than cycling the furnace against a condition it cannot clear.
- Safety opensLimit or rollout circuit breaks
- Code reportedThe open circuit is displayed
- Interval passesThe condition does not clear
- LockoutThe control refuses further trials
| Status code | What the control is saying | What it implies for you |
|---|---|---|
| Code 33 | The safety circuit is open now | Airflow checks are worth making |
| Code 13 | It stayed open, so heating is locked out | Stop resetting and arrange service |
| Both in sequence | The fault persisted through the wait | Report the order they appeared in |
A lockout is information, not an obstacle
Homeowners meet a lockout as an inconvenience: the furnace will not run and the thermostat is being ignored. Read from the control's side it is the opposite. The furnace has already tried, has already reported, and has now concluded that continuing to try is worse than stopping. Every attempt at heat with a safety circuit open is an attempt to fire a burner behind a device whose whole purpose is to say no.
That is why the useful response to code 13 is not to find the reset. It is to capture the sequence. Which code came first, how long the furnace ran before it dropped out, whether the blower kept moving air, and whether the pattern had been building over weeks are all facts the control does not store and the technician cannot reconstruct.
Two branches at opposite ends of the risk scale
Carrier names the limit switch and the flame rollout switch in the same entry because they sit in one series circuit, and the control cannot tell which of them opened. Those two devices sit at opposite ends of the risk scale. A high-limit opening on a loaded filter is a nuisance with an easy explanation. A rollout opening means heat reached a place the design does not put heat, and the questions that follow concern the heat exchanger and the venting.
Until a technician establishes which device is open, the higher-risk reading governs what you do. That is a single rule with a single consequence: no resets, no panel removal, and no running the furnace to see whether it behaves. The furnace limit switch explainer covers why the blower continues after the burners stop, and the air filter guide covers the one airflow check an owner can make safely.
What to give the technician
Hand the technician the furnace model and serial number from the rating plate, both status codes in the order they appeared, the filter size and condition, how long cycles ran before dropping out, and whether soot or odour was present.
Safe homeowner checks
- With the furnace switched off, inspect the return-air filter and fit a clean one of the specified size and type if it is loaded.
- Walk the house and confirm that supply registers and return grilles are open and not covered by furniture, rugs, or stored items.
- Record the flash pattern through the sight glass without opening the blower door, along with the date and time of the lockout.
Is a reset appropriate?
Carrier's control clears a lockout on its own after a fixed interval, so an automatic retry proves nothing about the underlying condition. Interrupting power to force an earlier retry removes the record without changing the circuit.
When to call a technician
- Identifying which safety device opened, measuring temperature rise, and inspecting combustion and venting are licensed gas-furnace tasks.
- Treat soot, scorching, an odour of combustion products, or a carbon monoxide alarm as an immediate stop. Get fresh air into the space, keep the appliance off, and use the emergency number your gas supplier publishes.
Questions people ask about this
How long does a Carrier lockout last?
The two-stage control described in this guide releases an ignition lockout automatically after three hours. A safety-circuit lockout behaves in the same spirit: the wait is a designed pause, not evidence that the fault has gone.
Can I clear code 13 by turning the power off?
Interrupting power clears the stored code. It does not close an open safety circuit, and it destroys the sequence a technician would have used to see how the fault developed.
Why does the blower keep running with no heat?
Continued airflow after the burners stop is the control removing heat from the exchanger. It is a cooling response to the safety opening rather than a sign that the blower or the thermostat caused the fault.
Is a dirty filter enough to cause this?
Restricted airflow can raise furnace temperature until the high-limit branch opens, and a repeat of that can end in lockout. It cannot account for a rollout opening, which is why the code is not treated as a filter problem on its own.
Evidence recordHow this page was checked
service manual, official manufacturer support article · checked 2026-09-15
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Carrier technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- service manual, official manufacturer support article
- Scope of the definition
- Carrier deluxe two-stage gas-fired induced-combustion furnaces with PSC or ICM blower motors, as covered by troubleshooting guide 58-3T
- Last checked
- 2026-09-15