Goodman furnace 3 amber flashes: Second stage heat called with no first stage call
Three amber flashes means the thermostat is calling for second stage heat without calling for first stage. That is not a valid combination, and it points at the thermostat or its wiring.
Applies to: Goodman GMEC96 and Amana AMEC96 two-stage gas furnaces with a three-colour diagnostic LED.
What it means
A two-stage furnace expects its thermostat to call for first stage heat and then, if more output is needed, add second stage on top. A second stage call arriving without a first stage call is not a sequence the furnace can act on, so the control flags it. This is a wiring or configuration fault rather than a mechanical one: the furnace is working correctly and reporting that it has been given contradictory instructions. It appears most often after a thermostat has been replaced, particularly where a single-stage or incorrectly configured thermostat has been fitted to a two-stage furnace.
Most common causes
- A thermostat wired incorrectly, with the second stage heat wire connected but not the first.
- A single-stage thermostat fitted to a two-stage furnace and wired to the second stage terminal.
- A thermostat configured for the wrong equipment type.
- A broken or disconnected first stage heat wire, so only the second stage call arrives.
- A zone control board sending stage calls in the wrong order.
- A smart thermostat set up without specifying two-stage heating.
How to diagnose it
- Establish whether the thermostat has been replaced or reconfigured recently. This code following a thermostat change is the usual story.
- Confirm the colour is amber and not red. Note that amber is not a guarantee of normal operation on this control — this code and the four amber flash code are both faults, even though one and two amber flashes are normal heating.
- Note whether the furnace heats at all, and whether it seems to run only at full output.
- Check whether the thermostat is configured for two-stage heating in its own settings menu.
How to fix it
- Have the thermostat wiring checked against the furnace's terminals. This is the most common cause and is quickly resolved.
- Configure the thermostat for two-stage heating if it supports it, or fit one that does.
- If a wire has broken between the thermostat and the furnace, that needs tracing — technician work, though not an alarming fault.
- If a thermostat was recently installed, call whoever installed it. This is a configuration error rather than a furnace fault.
Notes
Two-stage furnaces fitted with thermostats that do not understand staging are common, and the furnace often appears to work — it simply never uses its low stage, which is where its efficiency advantage lives. This code catches that.
Related
All codes for this manufacturer
Goodman and Amana furnace fault codes — every code, with what differs between models.