Rheem Rheem R96V 96% AFUE Two-Stage Variable Speed Upflow Gas Furnace 4 FLASH Error Fix: Pressure Switch Stuck Open

Error code 4 FLASH on the Rheem Rheem R96V 96% AFUE Two-Stage Variable Speed Upflow Gas Furnace means: Pressure Switch Stuck Open. The inducer motor is running but the pressure switch has not closed within the allotted time. This is the single most common Rheem furnace fault code. The inducer is creating draft, but insufficient negative pressure is reaching the pressure switch. Causes include: blocked exhaust vent pipe (check the vent termination outside for ice, bird nests, wasp nests, leaves, or debris), blocked condensate drain line or trap (condensing furnaces — water backup prevents proper venting), cracked or disconnected pressure switch hose, kinked or deteriorated rubber hose, a weak or failing inducer motor that cannot generate sufficient draft, or a faulty pressure switch with incorrect actuation pressure. Inspect the entire vent run. Clean the condensate trap. Test the pressure switch with a manometer against its rated actuation pressure.

The most successful fix is "Test and Replace Pressure Switch or Inducer Motor" (hard difficulty, ~90 minutes). Estimated DIY cost: $20-$40. HomeMD has 2 community-ranked fixes for this error.

This error is rated warning severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Yes — the top-ranked community fix ("Test and Replace Pressure Switch or Inducer Motor") is rated hard difficulty and takes about 90 minutes. Tools needed: T20 Torx screwdriver, Manometer, Clamp meter, Multimeter.

DIY cost: $20-$40. Professional repair typically costs $250-$400. Many homeowners save money by trying the top-ranked community fix first.

The Rheem Rheem R96V 96% AFUE Two-Stage Variable Speed Upflow Gas Furnace has 8 other known error codes, including: 1 FLASH (Normal — Heat Call Active), 10 FLASH (Rollout Switch Open), 11 FLASH (High-Stage Pressure Switch Open (Two-Stage Only)), 2 FLASH (System Lockout — Ignition Failed), 3 FLASH (Pressure Switch Stuck Closed), and 3 more.

Error code 4 FLASH also appears on 2 other Rheem models: Rheem Professional Classic 50 Gal. 38,000 BTU Natural Gas Water Heater, Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace. The fix may vary by model, so check each model's specific page for tailored repair steps.