Carrier AC / Heat Pump Error 13 – Causes & Fix
A limit or rollout switch stayed open too long, so the furnace has locked itself out for 3 hours.
Safety first · Consult a professional
Don't press the button on a flame rollout switch and don't keep cycling power to force heat – a tripped rollout means flames left the burner area, and the reason can send carbon monoxide into your home. Any smell of gas means leaving the house immediately, with no switches or phones used indoors, and calling 911 or the gas utility from the street; if a CO detector alarms, get everyone outside, call 911 and keep the furnace off until a professional has inspected it.
- Gas appliance: no DIY repairs. If you smell gas, leave the building, do not use switches and call your gas utility’s emergency line from outside.
- Carbon monoxide is odorless. Keep a CO alarm near fuel-burning appliances; if it sounds, get everyone outside and call 911.
- Unplug the appliance or switch off the breaker before opening any panel. Mains voltage can kill.
At a glance
Severity: High
- Meaning
- Limit Circuit Lockout – 3-Hour Shutdown (13)
- Typical repair cost
- $100–$4,000
- DIY difficulty
- Easy
Code 13 – one short flash and three long flashes – is the Carrier control giving up on the limit circuit rather than a brand-new fault. It appears when the main limit, the draft safeguard switch on 80% furnaces, the flame rollout switch or a blocked vent switch has stayed open for more than 3 minutes, or when a two-stage furnace has tripped its limit 10 times in a row on high heat. The board then refuses to light the burners and only resets itself after 3 hours. A lockout caused by the main limit usually traces back to the same airflow problems behind code 33, but the rollout and blocked vent switches do not close again on their own: they need a manual reset by a technician, so the furnace stays down until someone finds out why flames or flue gas escaped. That is why repeated 13 lockouts call for more caution than a single 33 – a blocked flue or a cracked or restricted heat exchanger can be behind them, and both can put carbon monoxide into the living space.
How it looks on the display
Model families & display variants
| Model family | Shows | Note |
|---|---|---|
| Single-stage 80% furnaces (58STA type) | 13 | Triggered when the limit, draft safeguard or flame rollout switch stays open for more than 3 minutes. |
| Condensing furnaces (59SC5 type) | 13 | Limit or rollout switch, or a blocked vent switch on models equipped with one. |
| Two-stage and variable-speed furnaces | 13 | Also set after 10 consecutive limit trips during high heat; the board keeps recent codes but erases them after 72 hours. |
| Infinity and Evolution communicating systems | Lockout message on the wall control | The wall control describes the limit lockout in text, which is handy if you missed the LED. |
Symptoms
- LED blinks once briefly, then three times slowly, over and over
- No heat for hours – the thermostat calls, but the furnace doesn't even try to start
- Earlier the furnace was turning on and off every few minutes (often code 33)
- Heat returns by itself after about 3 hours, then the lockout happens again
- Soot, scorch marks or discolored metal visible near the burners through the sight glass
- CO alarm chirping or alarming, or headaches and nausea in the household when the furnace runs
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Airflow problem that keeps the main limit open – very dirty filter, blocked returns, failing blower or capacitor
- Flame rollout switch tripped by a blocked flue, restricted heat exchanger or starved combustion air
- Blocked vent switch or draft safeguard switch open – obstructed chimney or vent, downdraft
- Blower not running at all – failed motor or control, so heat has nowhere to go
- Cracked or internally blocked heat exchanger
- Defective limit switch or broken wire in the limit circuit
Fix it step by step
Record the code and what led up to it
Note the 1-short, 3-long pattern through the sight glass before touching the blower door, since removing it cuts power. Write down whether the furnace had been short-cycling or flashing 33 earlier and how many times it has locked out so far.
Tools: Flashlight
Look for danger signs before anything else
Check whether any CO alarm has sounded, whether there is soot or a scorched look around the burner compartment, or whether the area smells like exhaust. If you see any of these, leave the furnace switched off at its service switch, ventilate or leave the house as needed, and don't attempt a reset.
Tools: Flashlight
Rule out a choked airflow path
Swap a clogged filter, and make sure the big return grilles aren't blocked by furniture and the supply registers are open. If you do find a badly plugged filter, it is a believable explanation for a single lockout.
Check the venting you can see
Outside, make sure the PVC intake and exhaust on a condensing furnace are open and free of snow or nests. Indoors on an 80% furnace, look at the metal flue connector between furnace and chimney for a pipe that has slipped apart or rusted through – only look, don't handle it.
Tools: Flashlight
Allow one reset at most
If you corrected an obvious problem and found no warning signs, one power reset at the service switch lets you skip the 3-hour wait. If the furnace locks out again, doesn't light at all afterwards, or you found nothing to correct, stop resetting: a tripped rollout switch or a venting fault is likely and needs a technician.
Brief the technician
Tell them the code, how often it has locked out, whether 33 came first, what the filter looked like and whether wind, cold or CO alarms were involved. Ask specifically for the rollout switch, flue and heat exchanger to be checked if the lockouts keep repeating.
How to reset 13
- The control clears the lockout by itself after 3 hours and tries again
- After fixing a clear airflow problem, you can instead turn the thermostat off and switch the service switch off for 30 seconds, then on
- If 13 returns or the burners don't light afterwards, leave the furnace off – rollout and blocked vent switches are reset by a technician only
Where the parts are
- 1Fan
- 2Temperature sensor
- 3CAN bus
- 4Outdoor unit
- 5Compressor
- 6Engine computer (ECM)
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Technician diagnostic visit | No | $100–$200 |
| Limit switch replacement | No | $150–$350 |
| Rollout switch replacement plus correcting the venting or burner cause | No | $200–$600 |
| Blower motor replacement | No | $450–$1,200 |
| Heat exchanger replacement (often weighed against a new furnace) | No | $1,500–$4,000 |
Rough US estimates; technician call-out fees vary by region. Not a quote.
When to call a technician
Call a licensed HVAC technician after the second lockout, immediately if no airflow problem was found, and at once – with the furnace off – if a CO alarm sounded or you saw soot or scorching. Expect the technician to check which switch in the limit circuit opened, inspect the flue and burners for rollout causes and examine the heat exchanger, since a cracked one usually means replacing the exchanger or the furnace.
Frequently asked questions
Should I just wait out the 3 hours?
Waiting is safe, but it only buys time – the lockout will repeat if the cause is still there. Use the pause to check the filter and look for warning signs, and call for service if it locks out again.
Can I press the reset button on the rollout switch myself?
No. A rollout switch trips when flames come out of the burner area, which points to a blocked flue, a restricted or cracked heat exchanger or a combustion-air problem. Resetting it without finding the cause can expose the household to carbon monoxide.
Is code 13 a carbon monoxide risk?
Not always – a very dirty filter can cause it too. But repeated lockouts, especially involving the rollout or vent switch, are among the few furnace codes where CO is a real concern, so working CO alarms near bedrooms and a technician visit are important.
What's the relationship between code 33 and code 13?
Code 33 is the limit circuit opening; the furnace keeps retrying. If the circuit stays open longer than 3 minutes, or on two-stage models trips 10 times in a row on high heat, the control escalates to 13 and locks out.
Sources
- Official Carrier user documentation and support pages (facts only; wording is our own)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy