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?

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.

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.

Rheem Furnace 2 Flashes — Pressure Switch Fault

Need this fixed instead of diagnosed?

Price the common parts before you book service.

Run capacitor

Flame sensor

Igniter

Control board