Rheem Furnace 2 Flashes — Pressure Switch Fault
2 flashes on a Rheem furnace LED diagnostic light means a pressure switch fault. On most Rheem/Ruud models, the 2-flash code indicates the pressure switch did not close after the inducer motor started, or it opened during operation.
The pressure switch is a safety device that confirms the induced draft blower is creating adequate negative pressure before allowing ignition. If draft isn’t proved, the furnace won’t light gas.
Rheem 2-Flash Fault Scenarios
| Scenario | Meaning |
|---|---|
| Switch stuck open | Inducer running, no draft sensed |
| Switch stuck closed | Welded contacts, false signal before startup |
| Intermittent fault | Switch opens during run due to fluctuating draft |
Step-by-Step Diagnosis
Step 1 — Confirm Inducer Is Running
Turn the thermostat to heat and listen. Within 30 seconds, you should hear the inducer motor spin up (a moderate rushing/blowing sound). If you hear nothing from the inducer:
- Check that there’s power at the inducer motor terminals (should be 120V when the furnace calls for heat)
- A dead motor means no draft, which means no switch closure — fix the motor first
Step 2 — Check the Condensate Drain
Rheem 90%+ efficiency furnaces (RGPS, RGPH, RGTT series) produce condensate. The drain can:
- Back up into the inducer housing
- Block the pressure switch hose barb
- Fill the pressure switch itself with water
Disconnect the drain line at the trap and blow it clear. Check the small hose that connects the inducer to the pressure switch — if water is in the hose, drain it out.
Step 3 — Inspect All Pressure Switch Hoses
Trace every rubber hose from the inducer housing to the pressure switch(es). On Rheem 2-stage furnaces, there may be two pressure switches. Check for:
- Cracks or splits, especially at barb connections
- Hoses that have slipped off the barb
- Kinked hoses around wire bundles
- Hoses that have hardened and cracked from age
Step 4 — Test the Pressure Switch
With power off, use a multimeter on continuity across the pressure switch terminals. At rest with no suction:
- Should read open (no continuity)
Apply gentle suction to the hose barb (by mouth or small vacuum pump) while reading continuity:
- Should close (read continuity) when suction is applied
- If it doesn’t close under suction: replace the switch
Step 5 — Check the Flue Pipe
Walk outside. Look at the exhaust and intake pipes (PVC on 90%+ models). Any blockage — bird nest, ice, debris, or a collapsed fitting — will prevent draft, causing 2 flashes. Clear any obstruction.
Step 6 — Check for Negative Pressure Problems
If all the above checks out and 2 flashes persists, the inducer may not be generating enough suction. A tech can verify with a manometer at the switch port — should be -0.5 to -1.5” WC on most Rheem models. Low values indicate a worn inducer or housing leak.
Common Rheem Pressure Switch Part Numbers
| Model | Switch P/N |
|---|---|
| RGPS (80%, single stage) | 70-24068-03 |
| RGPS (80%, 2-stage) | 42-25197-03 |
| RGPH (90%+) | 42-25202-01, 42-25202-02 |
| RGTT (90%+) | Check label inside cabinet |
Parts to Have Ready
| Part | Cost |
|---|---|
| Pressure switch (OEM) | $25–65 |
| Pressure switch hose | $5–15 |
| Inducer motor assembly | $150–350 |
| Condensate trap | $15–30 |
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?
Finding the right replacement parts for your equipment is critical to getting it running again. Check current prices on Amazon — prices and availability change frequently.
2 Flashes vs. 3 Flashes on Rheem
- 2 flashes = Pressure switch fault (primary topic here)
- 3 flashes = Pressure switch stuck closed (different problem — switch welded or condensate in switch)
- 4 flashes = Open high-limit switch (overheating/airflow problem)
Always confirm your specific model code chart — posted on the inside of the furnace door or in the user guide.
See Also
- Rheem Furnace 5 Flashes Error Code — Flame Sensor Fault Fix
- Rheem Furnace 8 Flashes Error Code — Causes & Fix
- Rheem RGPS Furnace Error Codes — Flash Code Diagnostic Guide
- Rheem Furnace Error Code 57 — Causes & Fix