8 flashes = Combustion air / intake blocked. FVIR intake screen is restricted. The #1 cause: clogged screen at the base of the unit.
How to clean the intake screen
- Turn gas knob to "Off"
- Look at the bottom edge of the unit — the perforated metal ring is the intake screen
- Vacuum thoroughly with brush attachment
- For heavy buildup: compressed air or soft brush
- Don\'t use water
- Turn gas back on; relight pilot
- Monitor LED — should return to 1 flash
Resolves 80% of 8-flash issues. Clean annually.
Other causes
- Combustion air switch failure — replace switch
- Wiring fault between switch and gas valve
- Heavy carbon on burner (dealer cleaning)
- FVIR sensor false positive — sensor replacement
FVIR explained
Flammable Vapor Ignition Resistant — federal 2003 mandate. Screen prevents combustion of flammable vapors near floor (gasoline, paint thinner). Safety feature working as designed.
Bottom line
Clean the intake screen — 5-min DIY fixes 80% of cases.