Furnaces

No fault stored

Shown when the stored-fault history has been cleared, or after a power interruption wiped the last code. Not a fault by itself.

Blower on after power-up

The control powered up while a heat call was present (or after a power blip) and runs the blower for a short period before resuming normal sequence.

Limit circuit lockout

The limit circuit opened repeatedly or stayed open too long, so the control locked out gas heat. It follows repeated code 33 events.

Ignition lockout

The control tried to light and prove flame several times and failed every time, so it locked out. On these boards it usually auto-resets after about 3 hours.

Gas heating lockout

The control detected a gas-valve circuit problem and locked out heat. This lockout does not reset by itself.

Flame sensed with gas valve off

The control proved a flame while the gas valve was supposed to be closed. Treat it as a gas valve or flame-circuit hazard; confirm on the door legend for your model.

Pressure switch did not open

At the start of a call, the pressure switch was already closed before the inducer ran, so the control will not start the sequence.

Low-voltage fuse open

The fuse protecting the 24 V control circuit on the board has blown.

Pressure switch did not close or reopened

The inducer was started but the pressure switch never proved draft, or it opened during the cycle.

Draft safeguard / low-heat pressure / auxiliary limit open

On some models a draft safeguard switch, low-heat pressure switch or (downflow units) auxiliary limit opened. Exact meaning depends on the model.

Limit circuit fault

A safety in the limit string (main limit, rollout, draft safeguard or blocked-vent switch, depending on model) opened. The blower runs to cool the unit before retrying.

Ignition proving failure

The igniter worked and gas was called for, but the control did not sense flame (or not enough) within the trial time. After several tries it becomes code 14.

Blower outside valid speed range

The control reports that the blower motor is not reaching or holding its commanded speed.

Inducer outside valid speed range

The variable-speed inducer is not running at the speed the control expects.

Pressure switch calibration fault

On variable-speed condensing units, the control could not calibrate the pressure switch at the expected inducer speed. On some two-stage models this code instead means the low-heat pressure switch is open.

Control circuitry lockout

The control detected an internal fault and locked out; it may auto-reset after about an hour.

Ignition failure / lockout

The furnace failed to light or prove flame on its retries and has locked out.

Pressure switch stuck closed

The pressure switch reads closed before the inducer starts, so the sequence will not begin.

Pressure switch stuck open

The inducer runs but the pressure switch never closes, so the furnace will not ignite.

High limit open

The main limit opened because the heat exchanger area got too hot, usually from low airflow.

Flame sensed with no call for heat

Most sources list this as flame detected while the gas valve should be closed. Some older Amana boards use 5 flashes for an open rollout switch, so check the door legend.

Rollout switch open (varies by board)

Two blog sources list this as an open flame rollout switch; one Amana listing uses 6 flashes for reversed polarity instead.

Low flame signal

Flame is present but the signal reaching the board is weak.

Board-specific (igniter / lockout / pressure switch cycling)

Sources disagree: listed as igniter circuit fault, ignition lockout, or pressure switch opened several times in one call (Amana HSI-2/50A55).

Reversed line polarity

The 120 V hot and neutral are reversed at the furnace, so flame sensing does not work correctly.

Internal control failure

The LED stays lit without flashing, indicating the control has failed internally.

Low pressure switch failed open

The low-fire pressure switch did not close when the control expected it to. Confirm against the legend on your furnace door.

Pressure switch calibration unsuccessful

The control could not calibrate the pressure switch at startup.

Flame sensed out of sequence

Flame is sensed when the gas valve should be closed.

Limit switch circuit open

A limit in the safety string opened, usually from overheating; the unit waits and retries.

Igniter circuit fault

The control detected a problem in the hot surface igniter circuit.

Indoor blower cannot start

The blower motor failed to start, for example from an obstructed wheel or seized bearings.

Inducer overcurrent

The combustion air inducer is drawing too much current.

Reversed line polarity

Line voltage hot and neutral are reversed (some boards also flag a poor ground).

Normal heat operation

Both LEDs flashing fast together show a heat call in progress.

Pressure switch open

The pressure switch did not close (some boards: opened repeatedly in one call). Often a vent or inducer issue.

Board failure or miswiring

Both LEDs steady on means the control failed or is wired incorrectly.

Low flame signal

Flame is present but the signal is weak.

Primary or secondary limit open

A high-temperature limit is open, usually from restricted airflow.

Power on, no heat call

Both LEDs flashing slowly together is the normal powered-up idle state.

Watchguard lockout

The control locked out after repeated failed ignitions or flame losses (Watchguard) and will retry after a timed delay.

Lockout or flame failure (varies)

One source lists a one-hour lockout after failed ignition; another lists low or no flame signal.

Pressure switch open

The pressure switch did not close when the inducer ran.

Limit switch open / overheat

The high limit opened because of overheating, usually low airflow.

Lockout: ignition retries exceeded

The furnace failed to establish flame on its allowed retries and locked out.

Pressure switch fault

The pressure switch is not in the expected state for the sequence.

Open limit / over-temperature

A high-temperature limit opened, usually from restricted airflow.

Flame sensed with no gas valve signal

The control sees flame when there should be none.

Reversed polarity or poor ground

Line voltage polarity is wrong or the ground is poor.

Gas valve circuit error

The control detected a fault in the gas valve circuit.

Low flame sense signal

Flame is proving but with a weak signal.

Igniter problem (varies by board)

Two sites list this as an igniter fault; another lists an open inducer limit on some boards.

Normal: heat call

A fast steady blink means the control sees a heat call and is running its sequence.

No power to the control

With the LED dark, the board is not powered.

Normal: no heat call

A slow steady blink is normal standby with no call for heat.

Control failure

The LED is on without flashing: the control board has an internal problem.

Flame present with gas valve off

Flame is sensed while the gas valve is not powered.

Pressure switch stuck closed

The pressure switch reads closed before the inducer runs.

Pressure switch stuck open

The pressure switch did not close after the inducer started.

High limit open (some boards: 24 V fuse open)

The main limit opened; one source notes some boards also use this code for an open low-voltage fuse.

Rollout or auxiliary limit open

A flame rollout switch or auxiliary limit opened. Rollout switches are often manual reset.

Lockout: no ignition

The control failed to light after its tries and locked out; it retries after about an hour.

Low flame signal

One source lists this as a possible low flame signal; check the sensor rod.