How do you fix Goodman EF?

Clearing a blocked condensate drain or emptying a backed-up pump reservoir is reasonable homeowner work and resolves most instances of this code. A frozen condensate line needs thawing and then insulating or rerouting, or it will freeze again on the next cold night. Full steps and safety notes are on this page.

Goodman furnace EF: Auxiliary switch or input is open

EF means a device wired into the furnace's auxiliary safety input has opened the circuit. What that device is depends entirely on how the furnace was installed.

Applies to: Goodman GMVC96, GMVM97, GCVM97 and Amana AMVM97 series gas furnaces with a two-character alphanumeric display. This code does not appear in the Goodman GCVC96 or Amana AMVC96 tables, so a furnace of either of those models does not produce it. Goodman describes it as an auxiliary switch open on GMVC96 and as an auxiliary input open on the modulating boards.

What it means

The control provides an auxiliary input so that an additional safety device can stop the furnace. What gets wired into it varies by installation: most often a condensate overflow switch, sometimes an auxiliary limit, occasionally an external interlock. This makes EF unusual among fault codes — it does not identify a specific component, because the component is whatever the installer connected. The most common single cause by a wide margin is a condensate overflow switch, which trips when the drain system backs up and water rises where it should not. That is a real fault worth catching: an unchecked condensate overflow will eventually find the electronics or the floor.

Most common causes

A condensate overflow switch tripped because the drain line or trap is blocked.
A full or overflowing condensate pump, or a pump that has failed.
A frozen condensate line on an installation where it runs through unheated space.
An auxiliary limit switch that has opened.
A wiring fault or loose connection in the auxiliary circuit.
An external interlock device tied into the input, depending on the installation.

How to diagnose it

Look for water first. A wet furnace base, a full condensate pump reservoir, or water around the drain is the usual answer.
Check whether the condensate drain line is blocked or, in cold weather, frozen where it passes through an unheated area.
Check whether a condensate pump is running when it should. A pump with a failed float or a blocked outlet backs up quickly.
Establish what is actually wired to the auxiliary input if the furnace has an installation record. On an unfamiliar installation a technician will trace it.

How to fix it

Clearing a blocked condensate drain or emptying a backed-up pump reservoir is reasonable homeowner work and resolves most instances of this code.
A frozen condensate line needs thawing and then insulating or rerouting, or it will freeze again on the next cold night.
A failed condensate pump is replaced — straightforward work, though it is plumbing plus electrical.
If no water is present, the auxiliary circuit needs tracing by a technician, since what is connected varies by installation.
Do not bypass the switch to restore heat. It is usually protecting against water reaching the furnace's electrical components.

Notes

Because the auxiliary input has no fixed meaning, this is one code where knowing your own installation matters more than knowing the code. If a technician has been to the furnace before, asking what is wired to the auxiliary input is worth doing while everything is working.

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

EF is the one code on this display whose price cannot be tabled in advance, because the circuit is a socket, not a component: the cost follows whatever device the installer wired into it, and the page above is honest that this varies house by house. The knowable parts: the $75–150 diagnostic (repair cost guide) identifies the device and why it opened, and the repair then belongs to that device's own economics — often modest, since auxiliary safeties tend to be inexpensive switches guarding cheap-to-fix conditions. The costly mistake is treating the input as the problem: a safety device that opened is usually a messenger, and the bill for shooting it (bypassing the input) can eventually be measured in water damage or worse.

DIY or call a pro?

A homeowner can do real detective work here without touching anything: the installation invoice or manual for your specific system may say what was wired to the auxiliary input, and knowing that before the visit collapses the diagnosis. What remains professional is everything electrical — confirming which device opened, why, and whether it acted correctly. The bright line is bypassing: an EF input is somebody's deliberate safety decision from installation day, and jumpering it out because the furnace 'works fine otherwise' undoes a protection installed for a reason nobody on site may remember until it matters. If the device seems to trip for no reason, that is a diagnosis request, not a nuisance to silence.

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.