About & Methodology
FurnaceBlinkCode is a free, no-login utility that answers one question: "My furnace is blinking a light — what does it mean and what should I check first?" It is built and maintained by Real Tech Ventures LLC.
How the fault database is built
- Flash counts, fault meanings and part numbers are compiled from published OEM installation and service literature for 10 control-board families (Goodman/Amana/Daikin, Carrier/Bryant/Payne, Trane/American Standard, Lennox, Rheem/Ruud, York/Coleman/Luxaire/Evcon, ICP brands, Nordyne/Intertherm/Miller, Armstrong/Allied, Williamson).
- Where manufacturers use conflicting tables (for example Rheem's Table A vs. Table B), the tool shows both and gives a simple field test to tell them apart.
- Root-cause percentages are illustrative field-experience rankings meant to tell you what to check first; they are not statistical guarantees.
- Cost ranges are rough retail and flat-rate estimates and vary widely by region and contractor.
- Always compare against the wiring diagram and fault decal inside your own furnace door. Manufacturers change board vendors mid-series.
Multimeter benchmarks
Typical flame-sensor current of 1.5–6.0 µA DC, silicon carbide igniter resistance of roughly 40–90 Ω, silicon nitride of roughly 11–20 Ω, and capacitor tolerance of ±5% are commonly cited service values. Your furnace's own manual takes precedence. See the multimeter pass/fail tester.
When to stop and call a licensed HVAC professional
- A manual-reset flame rollout switch has tripped (this can indicate a cracked heat exchanger or blocked flue).
- You smell gas, see soot or scorching around the burner box, or a CO alarm has sounded. Leave the home and call your gas utility or 911.
- A limit switch trips repeatedly after you have replaced a dirty filter and opened all vents.
- You are not comfortable working near 120V wiring or gas lines.
- The same fault returns within days after a cleaning or part swap.
Never jumper, bypass or tape over a safety switch.
How the site is funded
The decoder is free. The site earns revenue from display advertising, occasional affiliate links to replacement parts, and an optional $14 printable Field Pack. Advertising and affiliate relationships never change a diagnosis. See our Privacy Policy.
Corrections
Found an error or have a door-decal photo for a board we don't cover? Contact us and we'll review it.