Carrier two-stage induced-combustion gas furnace fault codes (58DXT, 58UXT, WeatherMaker 8000 two-stage)
Every fault code for this Carrier two-stage induced-combustion gas furnace is below, with what it indicates and a verdict: whether you can safely check it or it is a call for a technician. Here the code is short and long flashes. The source is Carrier's own service manual. Confirm your model is on the list; other Carrier controls use different codes.
Before any code: if you smell gas or a carbon monoxide alarm is sounding, this is not a diagnostic exercise. Leave the house and call from outside. What to do about a gas smell or a CO alarm.
How to read the display
Carrier calls these status codes, and they are read differently from a plain flash count. Each code is a two-digit number: the first digit is the number of SHORT flashes, the second is the number of LONG flashes. A code 33 is three short flashes then three long flashes. The LED is viewed through a window in the blower-compartment door — do not remove the door while reading it, because that cuts the power and clears the code. A steady light is normal. This status-code system is used across many Carrier induced-combustion furnaces, and Bryant and Payne furnaces of the same era often use an equivalent one, but confirm the code list against the service label on your own furnace.
What each code means
Each code carries a safety verdict. Caution means there is a check you can safely make; pro-only means the correct repair is certified work and we do not walk through it here.
Continuous OFF — No light — no power to the control
No light — no power to the control
A dark status LED means the control is not getting power. The manual's first checks are for line voltage at the L1 and L2 terminals and 24 volts at the transformer secondary — in homeowner terms, whether power is actually reaching the furnace.
What you can do: Check the furnace switch and the breaker, and make sure the blower-door is seated so its safety switch is pressed in. If power is present and the light stays off, the control or transformer is a technician's diagnosis.
Rapid flashing — Reversed 115 VAC polarity
Reversed 115 VAC polarity
The line-voltage hot and neutral are reversed. The furnace will not run for heat until it is corrected, and on a twinned system the manual points to the twinning-kit instructions instead.
What you can do: This is line-voltage wiring for an electrician or the installer, especially if the furnace was just installed or serviced.
14 — Ignition lockout
Ignition lockout
The furnace failed to prove ignition and locked out. The control auto-resets after three hours, and the underlying failure is described under code 34.
What you can do: Confirm the gas is on and the filter is clean, and reset once at the thermostat. If it locks out again, it is the ignition fault under code 34 and needs a technician.
13 — Limit or flame roll-out switch lockout
Limit or flame roll-out switch lockout
A limit or flame roll-out switch stayed open long enough that the control locked out. It auto-resets after three hours, and the live condition behind it is code 33.
What you can do: Because a flame roll-out switch is involved, do not keep clearing this to run the furnace. See code 33 — it points at airflow, the blower, or a combustion fault a technician needs to find first.
21 — Gas heating lockout — no auto-reset
Gas heating lockout — no auto-reset
The control locked the gas heating out and, unlike most codes, will not reset itself. The manual's causes are a mis-wired gas valve or a defective control valve relay.
What you can do: A no-auto-reset gas lockout is a technician's diagnosis. There is no homeowner action.
22 — Abnormal flame signal — flame proved with the gas off
Abnormal flame signal — flame proved with the gas off
The control sensed flame while the gas valve was de-energized, and runs the inducer until the fault clears. The manual's causes are a leaky or a stuck-open gas valve.
What you can do: A gas valve that may not be sealing is a technician's job, promptly. If you also smell gas, leave and treat it as the emergency at the top of this page.
23 — Pressure switch did not open
Pressure switch did not open
The pressure switch stayed closed when the control expected it to open. The manual's causes are obstructed pressure tubing or a switch stuck closed.
What you can do: A stuck switch or its tubing is a technician's diagnosis, not a homeowner adjustment.
24 — Secondary voltage fuse is open
Secondary voltage fuse is open
The 24-volt fuse on the control has blown, which the manual attributes to a short circuit somewhere in the low-voltage wiring.
What you can do: Replacing the fuse without finding the short just blows the next one. Finding the short is a technician's job.
31 — High-heat pressure switch or relay did not close
High-heat pressure switch or relay did not close
On high-fire, the high-heat pressure switch or its relay did not close or reopened. The manual notes the control relay may be defective and otherwise refers to the long list under code 32.
What you can do: This is a sealed-switch, relay and venting diagnosis for a technician.
32 — Low-heat pressure / draft switch did not close
Low-heat pressure / draft switch did not close
A pressure, draft-safeguard or auxiliary-limit switch did not close or reopened. The manual lists a long set of causes — a restricted vent, improper vent sizing, a weak or failed inducer, excessive wind at the termination, obstructed tubing, a bad switch, or low gas pressure.
What you can do: The one safe check on that list is the outdoor vent termination — clear it of snow, leaves or a nest, and note whether a storm's wind could be blowing into it. Everything else on the manual's list is a technician's diagnosis.
33 — Limit or flame roll-out switch is open
Limit or flame roll-out switch is open
A limit or flame roll-out switch is open. The manual's first-listed causes are a dirty filter or restricted duct system; it also lists a loose blower wheel, a bad blower motor or capacitor, inadequate combustion air, and an open flame roll-out switch or fuse link, which require a manual reset. Left open past three minutes this becomes code 13.
What you can do: Start with the filter — it is the first cause the manual lists and the one you can fix. But if the flame roll-out switch is the one that tripped, do not keep resetting it: a roll-out is a combustion safety trip, and it needs a technician before the furnace runs again.
34 — Ignition proving failure
Ignition proving failure
The furnace lit but could not prove a strong enough flame, and will try three more times before locking out as code 14. The manual's causes include the gas being shut off, oxide build-up on the flame sensor, a failed hot-surface igniter, a bad ground, and low inlet gas pressure.
What you can do: Confirm the gas supply is on and the filter is clean, and reset once. Cleaning the flame sensor or testing the igniter is combustion and electrical work for a technician.
43 — Low-heat pressure switch open while high-heat is closed
Low-heat pressure switch open while high-heat is closed
The low-heat pressure, draft-safeguard or auxiliary-limit switch is open while the high-heat pressure switch is closed. The manual's causes are a pressure switch stuck open, disconnected or obstructed tubing, or low propane inlet pressure, and refers back to codes 32 and 33.
What you can do: This is a pressure-switch and tubing diagnosis for a technician.
45 — Replace control
Replace control
The control board has diagnosed its own internal fault and is calling for replacement. It reaches this only after the other checks in the troubleshooting guide have been ruled out.
What you can do: Replacing the integrated furnace control is a technician's job, and a good technician confirms the other causes are ruled out first rather than replacing the board on the code alone.
A note on brand names
We use the Carrier name only to identify which equipment these codes apply to. We are not affiliated with Carrier and are not an official support channel, and the code map above is written in our own words from the published service manual cited below.