Goodman furnace continuous on: Normal operation — no fault stored
A steady, unblinking LED means the control is powered and reporting no fault. If the furnace is not heating and the light is steady, the problem is usually not in the furnace.
Applies to: Goodman GMS, GMP, GMH, GMV8, GMV9, GMSS9 and Amana AMH, AMV9, AMSS9 series gas furnaces with a single red diagnostic LED. On communicating models such as GMVC96 and AMVC96 the equivalent indication is the code On.
What it means
A steady light is the control saying everything it monitors is satisfied. That is genuinely informative when the house is cold, because it narrows the search considerably: the furnace has power, its safety circuits are all closed, and it has no stored fault. What it usually means in that situation is that the furnace has not been asked to run. The request comes from the thermostat over the low voltage wiring, and a furnace that never receives a call for heat sits there perfectly healthy and perfectly idle. That is why a steady LED with a cold house points at the thermostat, its wiring, or its power rather than at the furnace itself.
Most common causes
- The furnace is running normally and there is no problem at all.
- The thermostat is not calling for heat — set to cool, set to off, or set below room temperature.
- The thermostat's batteries are flat, so it cannot close the heat circuit.
- A break in the low voltage wiring between the thermostat and the furnace.
- A thermostat that has failed or lost its programming.
- A thermostat wired incorrectly after a replacement, which is a very common cause of this exact symptom.
- A zone control board or damper system that is not passing the call through.
How to diagnose it
- Check the thermostat is set to heat and set above the current room temperature. This sounds obvious and is the answer often enough to check first.
- Replace the thermostat batteries if it takes them, even if the display still looks normal.
- Note whether the thermostat display shows a call for heat indicator. A thermostat that thinks it is calling and a furnace that shows no fault means the signal is not arriving.
- Note whether the fault followed a thermostat replacement or a smart thermostat installation. Miswiring, and particularly a missing common wire, produces exactly this.
- Check whether the furnace responds to the fan-on setting. If the blower runs on fan but nothing happens on heat, the heat wire is the suspect.
How to fix it
- Correct the thermostat setting or replace its batteries if that is the cause.
- If a thermostat was recently changed, have the wiring checked against the furnace's terminals. Smart thermostat installations without a common wire are a frequent source of intermittent no-heat calls.
- Low voltage wiring faults and zone control problems are technician work, though they are among the less alarming things a technician can find.
- If the furnace is heating normally, nothing needs doing. A steady light is what it should show.
Notes
It is worth knowing what normal looks like on your own furnace before something goes wrong. Checking the LED on a working furnace once takes a minute and makes every future reading meaningful, because a steady light means nothing if you do not know it was steady yesterday too.
Related
All codes for this manufacturer
Goodman and Amana furnace fault codes — every code, with what differs between models.