How do you fix Goodman LO?

Nothing to fix if the house is comfortable. If the furnace never reaches high stage in cold weather, have the second-stage circuit checked — the pressure switch codes cover this. Full steps and safety notes are on this page.

Goodman furnace LO: Low stage heat

LO means the furnace is running on low stage heat. It is normal and it is where a two-stage or modulating furnace spends most of its time.

Applies to: Goodman GMVC96 and GCVC96 and Amana AMVC96 two-stage gas furnaces with a two-character alphanumeric display. The modulating GMVM97, GCVM97 and AMVM97 boards have no LO code — they report heat demand as H followed by a percentage instead.

What it means

Low stage is the lower firing rate, and a well-matched furnace runs there for the large majority of the heating season. Seeing LO is confirmation the furnace is staging correctly rather than defaulting to full output. It is worth documenting mainly because it can be misread as underperformance: a furnace running at low output for hours while the house is comfortable is not struggling, it is doing the thing that makes a staged furnace worth having. The case that does warrant attention is a furnace stuck at LO in cold weather while the house fails to keep up, which points at a second-stage fault.

Most common causes

Mild to moderate conditions where low output meets demand. This is normal and expected.
The furnace staging correctly and not needing more output.
A second-stage pressure switch fault preventing the furnace from stepping up, which is the case worth investigating.
A thermostat not calling for second stage.

How to diagnose it

Note whether the house is comfortable. If it is, low stage running is correct.
Note whether the furnace ever steps up to high in genuinely cold weather.
If the house is not keeping up and the furnace stays at LO, look for a second-stage pressure switch fault.
Check the air filter and registers before assuming a staging problem.

How to fix it

Nothing to fix if the house is comfortable.
If the furnace never reaches high stage in cold weather, have the second-stage circuit checked — the pressure switch codes cover this.
Check the air filter and open closed registers if the house is not keeping up.
Do not assume low output means the furnace is failing. Long low-output runs are the design intent.

Notes

People often expect a furnace to blast heat and stop. A staged or modulating furnace deliberately does the opposite, and the resulting long gentle runs are frequently reported as the furnace not working properly.

All codes for this manufacturer

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

Models this code appears on

From the manufacturer's per-model database. If your model is not listed, this code may not exist on your board, or it may mean something different — check the model page.

What the fix costs

LO is where a healthy two-stage furnace lives, so most of the time this page costs nothing. The repair scenario is the furnace that stays at LO while the house loses ground in cold weather — on these boards that points at the second-stage circuit, and most often the second-stage pressure switch. Pressure switch work typically runs $150–400 per the repair cost guide, with the guide's standing caution attached: the switch is often reporting a real venting problem, so the visit should check the flue and condensate path before condemning the part. A thermostat that simply never calls second stage is cheaper still — configuration rather than parts.

DIY or call a pro?

Yours: the filter, the registers, and the one observation that matters — does the furnace ever step up to high fire in genuinely cold weather? A week of casual display-watching answers it. A professional's: everything in the second-stage chain, because proving whether the switch, the inducer's high speed, or the thermostat call is at fault means manometer readings on a running gas appliance. Do not jumper or bypass a pressure switch to test the theory; that switch is the furnace's proof it can vent combustion gases, and defeating it converts a comfort problem into a safety one.

What this looks like

From the outside, this usually shows up as there is no heat but nothing looks obviously wrong — that walkthrough covers what to check in order, and when it stops being a homeowner job.

Sources

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

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.