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4 FLASH

Rheem · Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace

Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace 4 FLASH Error Fix: Pressure Switch Stuck Open

The inducer motor is running but the pressure switch has not closed. This is the most common Rheem furnace fault code. Causes: blocked exhaust vent pipe (check the vent termination outside for ice, bird nests, debris), cracked or disconnected pressure switch hose, a weak inducer motor, or a faulty pressure switch. On the R801T (80% AFUE non-condensing furnace), also check for a blocked B-vent or chimney flue. Inspect the entire vent run from the furnace to the termination point.

warning2 fixes available✨ Free fix available

Quick Answer

Error 4 FLASH on the Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace means: Pressure Switch Stuck Open. The top-ranked community fix is “Test and Replace Pressure Switch or Inducer Motor” (hard difficulty, ~90 min, DIY cost: $20-$40). 2 community-ranked fixes available below.

Published February 2026 · 2 fixes · furnace

Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.

When to Call a Professional

While many furnace repairs can be done safely at home, consider hiring a qualified technician if:

The repair involves electrical wiring, gas lines, or refrigerant
You've tried the top-ranked fix and the error persists
You smell gas, see sparking, or notice water leaking
The repair requires specialized tools you don't have
Your appliance is still under manufacturer warranty

Average professional repair cost for this issue: $250-$400.

Other Rheem Models with Error 4 FLASH

Rheem Professional Classic 50 Gal. 38,000 BTU Natural Gas Water Heater

water_heater · 2 fixes

Rheem R96V 96% AFUE Two-Stage Variable Speed Upflow Gas Furnace

furnace · 2 fixes

Other Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace Error Codes

1 FLASH

Normal — Heat Call Active

Rollout Switch Open

System Lockout — Ignition Failed

2 fixes

3 FLASH

Pressure Switch Stuck Closed

2 fixes

5 FLASH

Flame Sensed Without Gas Valve Command

2 fixes

6 FLASH

Power Reversed or No Ground

Low Flame Signal

Igniter Circuit Failure

2 fixes

People Also Ask About Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace Error 4 FLASH

What does error code 4 FLASH mean on a Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace?

Error code 4 FLASH on the Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace means: Pressure Switch Stuck Open. The inducer motor is running but the pressure switch has not closed. This is the most common Rheem furnace fault code. Causes: blocked exhaust vent pipe (check the vent termination outside for ice, bird nests, debris), cracked or disconnected pressure switch hose, a weak inducer motor, or a faulty pressure switch. On the R801T (80% AFUE non-condensing furnace), also check for a blocked B-vent or chimney flue. Inspect the entire vent run from the furnace to the termination point.

How do I fix error code 4 FLASH on my Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace?

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.

Is error code 4 FLASH on a Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace serious?

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

Can I fix Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace error 4 FLASH myself?

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.

How much does it cost to repair Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace error 4 FLASH?

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

What other error codes does the Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace have?

The Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace has 8 other known error codes, including: 1 FLASH (Normal — Heat Call Active), 10 FLASH (Rollout Switch Open), 2 FLASH (System Lockout — Ignition Failed), 3 FLASH (Pressure Switch Stuck Closed), 5 FLASH (Flame Sensed Without Gas Valve Command), and 3 more.

Which other Rheem models have the 4 FLASH error?

Error code 4 FLASH also appears on 2 other Rheem models: Rheem Professional Classic 50 Gal. 38,000 BTU Natural Gas Water Heater, Rheem R96V 96% AFUE Two-Stage Variable Speed Upflow Gas Furnace. The fix may vary by model, so check each model's specific page for tailored repair steps.

What other error codes does the Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace have?

The Rheem Rheem R801T 80% AFUE Single-Stage Upflow Gas Furnace has 8 other known error codes:

1 FLASH — Normal — Heat Call Active (2 fixes)
10 FLASH — Rollout Switch Open (2 fixes)
2 FLASH — System Lockout — Ignition Failed (2 fixes)
3 FLASH — Pressure Switch Stuck Closed (2 fixes)
5 FLASH — Flame Sensed Without Gas Valve Command (2 fixes)
6 FLASH — Power Reversed or No Ground (2 fixes)
7 FLASH — Low Flame Signal (2 fixes)
8 FLASH — Igniter Circuit Failure (2 fixes)

Which other Rheem models have the 4 FLASH error?

Error code 4 FLASH also appears on 2 other Rheem models:

Rheem Professional Classic 50 Gal. 38,000 BTU Natural Gas Water Heater (water heater) · 2 fixes
Rheem R96V 96% AFUE Two-Stage Variable Speed Upflow Gas Furnace (furnace) · 2 fixes

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