Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
Rheem Furnace Error Code 57 — What It Means
Rheem furnace error code 57 indicates a low-stage pressure switch fault — specifically, the low-stage pressure switch failed to close (or opened unexpectedly) during the call for heat. On two-stage Rheem furnaces, the inducer motor runs at low speed first and the low-stage pressure switch must close to confirm adequate draft before ignition. Code 57 means the control board saw the switch remain open when it should be closed, aborting the ignition sequence. The furnace will lockout after repeated failed attempts.
Common Causes
- Blocked or kinked pressure switch hose — The rubber tubing connecting the inducer outlet to the pressure switch is the most common failure point; it collapses, clogs with condensate, or cracks over time.
- Failed pressure switch — The switch diaphragm fails mechanically and won’t close even with adequate draft pressure.
- Weak or failed inducer motor — If the inducer isn’t spinning at full speed, it can’t generate enough negative pressure to close the switch.
- Blocked flue or condensate drain — Blocked venting creates back pressure that prevents the switch from seeing correct draft differential.
Step-by-Step Fix
- Inspect the pressure switch hose — With the furnace off, locate the rubber hose(s) running from the inducer housing to the pressure switch. Check for kinks, cracks, or condensate blockage. Blow through it — it should be clear. Replace if cracked or blocked.
- Check for condensate in the hose — Tip the hose downward and drain any water. Condensate accumulation in the hose is a frequent cause of code 57 on high-efficiency models.
- Test the pressure switch — Use a manometer or a vacuum hand pump to apply suction to the switch port. The switch should click closed at the rated pressure (typically -0.6” to -1.0” WC for low stage). No click = failed switch.
- Verify inducer motor operation — Power the furnace and watch the inducer. It should reach full speed within a few seconds of call for heat. A humming motor that isn’t spinning, or slow rotation, means a failed inducer motor or capacitor.
- Reset the system — Cycle the thermostat off and back on after repairs. Clear the fault by restoring power. If code 57 persists after replacing the switch and hose, inspect the flue for blockage.
Parts Often Needed
| Part | Notes |
|---|---|
| Low-stage pressure switch | Match to exact model; Rheem/Ruud switches are model-specific |
| Pressure switch hose | Available at HVAC supply houses; measure ID/OD before ordering |
| Inducer motor assembly | Replace if motor is seized, humming, or capacitor has failed |
| Condensate drain trap | Clean or replace if blocked, which causes pressure switch issues |
Technician Tips
Modern furnaces use LED flash codes on the control board to diagnose failures. Before calling for service, count the number of flashes between pauses and check your owner’s manual for the code chart. The most common furnace error — 1-4 flashes usually means ignition failure — is often caused by a dirty flame sensor. The flame sensor is a $15-30 part that takes 10 minutes to clean. Remove it with a 1/4” nut driver, gently scrub the metal rod with emery cloth or a dollar bill (yes, a dollar bill — it’s the right abrasiveness), and reinstall. This fixes about 60% of “no heat” service calls.
DIY vs Pro: Error codes related to pressure switches (usually 2-3 flashes) often indicate blocked vents or condensate drains — safe to check yourself. Codes related to gas valves or ignition modules (4+ flashes) are best left to a licensed HVAC technician.
Need Replacement Parts?
Before ordering, match the furnace part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
If the inducer runs at full speed, the hose is clear, and a new pressure switch still gives code 57, the flue vent may be partially blocked or the heat exchanger may have a crack affecting combustion airflow. Both require a tech with combustion analyzer and inspection camera.