Goodman furnace 3 double red flashes: Second stage pressure switch stuck open, or an inducer error

Three double red flashes means the second stage pressure switch did not close when the furnace called for high fire. The furnace usually still runs on low fire, so the symptom is reduced output rather than no heat.

Applies to: Goodman GMEC96 and Amana AMEC96 two-stage gas furnaces with a three-colour diagnostic LED. This is a distinct pattern from three single red flashes, which signals the first stage.

What it means

A two-stage furnace carries two pressure switches, one per firing rate, because high fire moves considerably more combustion air and needs its own proof of draft. Goodman distinguishes the two failures by pattern rather than by count: three single flashes for first stage, three double flashes for second. The practical consequence of the second-stage version is distinctive — the furnace is not dead. It runs on low fire, which in mild weather may be perfectly adequate, so the fault often goes unnoticed until the weather turns and the house cannot keep up.

Most common causes

• The second stage pressure switch has failed and no longer closes.
• The sensing hose to the second stage switch is disconnected, kinked, or blocked.
• The inducer is not reaching high stage speed, so the switch never sees its rated pressure.
• A partly restricted vent or intake — adequate for low fire, insufficient for high fire, which is exactly why the fault appears only at second stage.
• A partly blocked condensate drain, which restricts more at the higher firing rate.
• The two pressure switches swapped during a previous repair.
• A wiring fault in the second stage switch circuit.

How to diagnose it

1. Confirm the pattern is double flashes rather than single. That distinction is what separates this from the first-stage code.
2. Note whether the house heats slowly rather than not at all, which fits this fault and rules out several others.
3. Check the outside vent termination — a partial restriction is exactly what produces a high-stage-only failure.
4. Check the condensate drain for slow drainage rather than complete blockage.
5. Note whether the fault followed a service visit, since swapped switches are a real cause.

How to fix it

1. Clear the vent termination and condensate drain if either is restricted. Both are within homeowner reach.
2. The pressure switches, hoses, and inducer are technician work.
3. Have the technician confirm the switches are fitted the right way round if the furnace was recently serviced.
4. Do not simply live with low fire and ignore the code. The partial restriction usually worsens and eventually affects low fire too.

Notes

Using a double-flash pattern to distinguish stages is unusual and easy to miss if you are counting quickly. Watching two or three full cycles of the pattern before deciding is worth the extra half minute.

Related

• 3 red flashes — First stage pressure switch stuck open
• 6 red flashes — Pressure switch cycle lockout

All codes for this manufacturer

Goodman and Amana furnace fault codes — every code, with what differs between models.

Sources

• Goodman Manufacturing — Diagnostic Code Identification System (model-specific fault code lookup)