Furnace Fault Codes

Goodman GMP / GMN / GMNT / GMPE / GMPH / GMPN / GMPV / GMT furnace fault codes

Every diagnostic code published for the GMP series — 8 of them — taken from the manufacturer's own per-model fault code database rather than from a general table.

Codes differ between models from the same manufacturer, which is why this list is worth reading in preference to a brand-wide one. No code below contradicts another Goodman model that publishes its own list. At 8 codes it is the shortest list of any Goodman board here; the GCVM97 publishes 43. The same board is sold as Goodman GMN / GMNT / GMPE / GMPH / GMPN / GMPV / GMT, with the same code list.

GMP fault codes

What the LED showsWhat it means
1 flashLockout after too many failed ignition attempts
2 flashesPressure switch is closed when it should be open
3 flashesPressure switch will not close
4 flashesHigh limit switch is open — the furnace is overheating
5 flashesFlame detected when no flame should be present
LED offNo power to the furnace, or an internal control fault
rapid flashingReversed 115 volt polarity, a grounding problem, or an open igniter circuit

Codes that are not faults

These 1 indications mean the furnace is doing something normal — running a stage, moving air for cooling, or sitting idle. They are listed separately so they do not get counted as problems.

What the LED showsWhat it means
continuous onNormal operation — no fault stored

Other models with their own code list

What the fix costs

For what a technician visit and this kind of repair typically runs, see the furnace repair cost guide.

What this looks like

From the outside, this usually shows up as the vents blowing cold air on a heat call — that walkthrough covers what to check in order, and when it stops being a homeowner job.

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.

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