Rheem Furnace 2 Flashes — Pressure Switch Fault

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

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

Parts to Have Ready

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

Related Articles

• Rheem Classic Series Furnace Error Codes — Complete Guide
• Rheem Air Handler E1 Error Code — Causes & Fix
• Rheem Furnace 3 Flashes Error Code — Causes & Fix
• Rheem Furnace 4 Flashes — Open High Temperature Limit Fix
• Rheem Furnace 5 Flashes Error Code — Flame Sensor Fault Fix