Equipment error code

Carrier code 13

Flame not sensed — the control energized the gas valve and igniter but did not detect flame at the flame sensor within the allowed trial window.

Equipment: furnace
Brand: Carrier
Source checked: 2026-03-01

What this code means

Flame not sensed — the control energized the gas valve and igniter but did not detect flame at the flame sensor within the allowed trial window.

Source: Carrier 59MN7 Service Instructions — Fault Code Definitions (099-35-04PY-0A) · checked 2026-03-01

Which models show it

Carrier/Bryant 59MN7, 59TN6, 59SC5A, 59SP5A, 58MCA, and 58MVP furnaces using the integrated control fault code table.

What is actually happening

You may hear the inducer and igniter, see a brief glow, then the gas valve closes and the furnace locks out. No sustained flame is proven to the board.

Is it safe to keep running?

Do not cycle the furnace repeatedly. Failed ignition attempts can accumulate unburned gas in the chamber on some designs.

Shut it down when

Stop if you smell gas, hear booming on ignition, or the unit locks out more than twice in one evening.

What a homeowner can safely check

Confirm the gas valve lever at the furnace is parallel to the gas pipe (on).
Check that other gas appliances work — if none do, contact the gas utility.
Replace a very dirty air filter; extreme airflow issues can affect combustion on marginal systems.
Ensure the front panel and door switches are seated — the furnace will not complete ignition with interlocks open.

When to stop

Any gas odor inside the home.
Visible soot or yellow flames when ignition briefly occurs.
More than two ignition attempts without heat.

Likely causes ranked

1. Dirty or corroded flame sensor rod
How a tech confirms: Measures microamps on the flame sensor circuit during a supervised ignition test; cleans or replaces the rod.
Typical repair: $150–$325 · Air Conditioner Repair cost guide
2. Failed hot-surface igniter or cracked igniter
How a tech confirms: Ohms the igniter; watches ignition sequence with meter on gas valve and HSI circuit.
Typical repair: $200–$450 · Furnace Replacement cost guide
3. Low gas pressure or closed gas valve
How a tech confirms: Manometer test at gas valve inlet; verifies valve coil and line shutoffs.
Typical repair: $175–$400 · Air Conditioner Repair cost guide
4. Faulty gas valve or integrated control board
How a tech confirms: Sequences valve and ignition outputs; compares to manufacturer resistance and voltage tables.
Typical repair: $400–$950 · Furnace Replacement cost guide

Is this the end of this unit?

If the heat exchanger is compromised or the furnace is past 18–20 years with a failed gas valve and board quote over ~$1,200, compare against replacement. Older single-stage units often fail economically.

How to clear the code

Power cycle at the furnace switch once after confirming gas supply and a clean filter. Wait five minutes before calling for heat again to allow any lockout timer to expire.

Why clearing is not fixing it: The board clears when it completes a successful flame-proving cycle. A weak igniter or dirty sensor will trip code 13 again on the next call for heat.

Which trade to call

Call a licensed hvac contractor who works on furnace equipment. Gas, refrigerant, and combustion faults are not general handyman jobs.

More codes from this brand

Symptom guide: Furnace Not Heating

FAQ

What is Carrier furnace error code 13?

Code 13 means the control did not sense flame after ignition within the trial period — a flame-proving failure, not a thermostat error.

Can I clean the flame sensor myself?

Homeowners can gently clean a flame rod with fine steel wool only if the gas is off and you follow the manual. Many prefer a technician because gas valve and high-voltage ignition are nearby.

How much does code 13 repair cost?

Flame sensor cleaning or replacement is commonly $150–$325. Igniter replacement runs $200–$450. Gas valve or board failures can reach $400–$950 plus diagnostic fees.

Does code 13 mean a gas leak?

Usually not — it means no flame was proven. If you smell gas, leave and call the utility. If ignition never lights, low gas pressure or a closed valve is possible.

Why does my Carrier furnace light then go out?

That pattern matches weak flame signal — dirty sensor, failing igniter, or draft issues. Code 13 is the stored fault for that sequence on many Carrier boards.

Source

Source — Carrier 59MN7 Service Instructions — Fault Code Definitions (099-35-04PY-0A). Checked 2026-03-01.