GOODMAN DIAGNOSTIC REFERENCE SINGLE RED LED — FLASH CODES DOC GOODMAN-4-FLASHES

Goodman furnace: Open Primary Limit Switch

Q: What does 4 flashes mean on a Goodman furnace?

Open Primary Limit Switch. The high-limit opened — the furnace overheated. The circulator blower runs until the limit closes. Code: four short flashes.

YOUR LIGHT: 4 FLASHES — MATCH IT ABOVE

Try DIY first, then call a pro

What does 4 flashes mean on a Goodman furnace? The high-limit opened — the furnace overheated. The circulator blower runs until the limit closes. Code: four short flashes.

GOOD NEWS: THE FIRST CHECKS ARE FREE AND TAKE MINUTES.

Try these first — in this order

Replace the filter and open every supply/return vent — 5 minutes.

1Check: Dirty filter or restrictive ductwork (official first cause)

Still showing the code? See every cause ↓ Get repair quotes near you

Repeated overheating cooks heat exchangers (a CO-risk precursor). Recurring code 4 = service call. DIY part cost: $5–25 / $10–25 — a pro visit for this class of fault typically runs $150–350.

What causes it (in order of likelihood)

Dirty filter or restrictive ductwork (official first cause) DIY-CHECKABLE
Faulty limit switch TECH
Weak blower motor or failed capacitor TECH

Parts referenced by this code

Air Filter (check size on the old one)

$5–25

Amazon HVACDirect

Blower Capacitor

$10–25 · Match µF + voltage printed on the old capacitor

Amazon HVACDirect

Always match parts against your model's parts list — part numbers vary within a series.

Applies to

GMS8 · GDS8 · GHS8 · GMSS96 · GMH8 · GDH8

Different Goodman generations use different code maps. If your series isn't listed, don't assume this meaning — check your blower-door label.

Verified against Goodman GMS8/GDS8/GHS8 Service Manual (RS6612006), p.42 — “four short flashes followed by a pause”

Verified against Goodman GMSS96 Service Manual, p.32

Last verified 2026-07-06 · how we verify