Igniter
Price the ignition part only after confirming the model number and connector.
Rheem Furnace 8 Flashes Error Code — What It Means
Eight flashes on a Rheem furnace status LED indicates an ignition lockout — the furnace attempted to light the burners the maximum number of times (typically 3 trials) without successfully proving flame, and the control board locked out to prevent gas accumulation. The board will remain in lockout until the condition is manually reset or the auto-reset timer (usually 1 hour) expires. This is one of the most common Rheem fault codes and in most cases is caused by a dirty flame sensor or weak ignitor.
Common Causes
- Dirty flame sensor — Oxide buildup on the sensor rod reduces the microamp signal below the board’s threshold; the burner lights but the board doesn’t see it.
- Weak or failing hot surface ignitor — An ignitor that glows but doesn’t reach ignition temperature will fail to light the burner consistently.
- Low gas supply pressure — Insufficient manifold pressure produces a weak flame the sensor can’t read reliably.
- Faulty gas valve — The valve opens but doesn’t fully deliver gas to the burners, causing inconsistent or no ignition.
Step-by-Step Fix
- Reset the furnace — Press the reset button on the furnace (often located on or near the control board) or cut power at the disconnect for 30 seconds and restore. This clears the lockout so you can observe the ignition attempt.
- Clean the flame sensor — Locate the single-rod sensor in the burner flame path. Remove it (one screw), buff the rod lightly with fine steel wool, reinstall, and retry ignition.
- Check the ignitor glow — Watch the ignitor during a heat call. It should glow bright orange/white within 20–30 seconds. Dull red or no glow = replace the ignitor.
- Test ignitor resistance — With power off, measure across the ignitor terminals. Silicon carbide ignitors typically read 40–100 Ω cold. Open circuit = defective.
- Verify gas pressure — Check manifold pressure with a manometer at the gas valve test port. Natural gas: 3.5” W.C.; LP: 10” W.C. Adjust regulator or call the gas utility if pressure is low.
- Reset and observe — After each repair attempt, reset the board, restore power, and watch the full ignition sequence through the sight glass.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame sensor rod | Universal or OEM; clean first before replacing |
| Hot surface ignitor | Match voltage (120V) and mounting style — Rheem commonly uses Norton/Saint-Gobain ignitors |
| Gas valve | Only replace after confirming pressure and wiring are correct |
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.
When to Call a Pro
If you’ve cleaned the sensor and replaced the ignitor but the furnace still locks out, have a technician check gas valve operation with a manometer and verify the control board is sending proper ignitor power voltage (typically 120V AC). Continued lockouts with a known-good sensor can indicate a cracked heat exchanger affecting combustion air — a CO risk.