Rheem / Ruud · Furnace error code

1 flashLockout or flame failure (varies)

Single source High-voltage / caution

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Related diagnostic guides

Guide · Furnace

Furnace blowing cold air on a heat call

The common causes are a fan set to ON, a dirty filter tripping the high limit so the burners stop while the blower runs, a full condensate drain on a high-efficiency furnace, or an ignition lockout. Gas valve and burner work is blocked; stop at diagnosis and refer.

4 steps ~45 minmoderate

Guide · Furnace

Furnace runs no heat (blower only or nothing)

Start with the board LED code, then work the call path: thermostat, 24 V, safeties, inducer, ignition, flame proving. Most no-heat calls end at a filter, a flame sensor, a pressure switch issue or gas being off.

5 steps ~45 minmoderate

Guide · Furnace

Furnace short cycling (starts and stops quickly)

Short cycling is usually a safety opening mid-cycle (limit from low airflow, flame sensor dropping out, pressure switch opening) or a thermostat issue. Read the code and time the cycle.

4 steps ~45 minmoderate

More Rheem / Ruud furnace codes

Rheem / Ruud · Furnace

2 flashes

Pressure switch open

Cross-checked High-voltage / caution

Rheem / Ruud · Furnace

3 flashes

Limit switch open / overheat

Cross-checked High-voltage / caution