Goodman furnace Ft: Field test mode

Ft means the furnace is in field test mode. It is a service mode, not a fault — but a furnace left in it will not behave normally.

Applies to: Goodman GMVM97 and GCVM97 modulating gas furnaces with a two-character alphanumeric display.

What it means

Field test mode lets a technician drive the furnace through its operating states without waiting for real demand, which is how commissioning and fault-finding are done efficiently. Seeing Ft on the display means the furnace is currently in that mode. That matters to a householder for one specific reason: a furnace left in field test mode after a service visit is not responding to the thermostat in the normal way, and the resulting behaviour — running when it should not, or not running when it should — looks like a fault. Establishing whether a technician has just visited answers this immediately.

Most common causes

A technician has deliberately entered field test mode.
The furnace was left in field test mode after a service visit.
Field test mode entered accidentally by pressing control buttons.
The mode entered during commissioning of a new installation and not exited.

How to diagnose it

Establish whether the furnace has been serviced or installed very recently. That is the answer in nearly every case.
Note that this is a mode rather than a fault — the furnace is not reporting a problem.
Note whether the furnace's behaviour seems disconnected from the thermostat, which is what field test mode produces.
Do not press control board buttons to try to exit it without knowing the sequence.

How to fix it

If a technician has just visited, call them. Leaving a furnace in field test mode is an oversight they should correct.
Field test mode normally times out on its own, so waiting is often sufficient.
A power cycle at the service switch usually returns the furnace to normal operation.
Do not experiment with control board buttons on a gas furnace to find the exit sequence.

Notes

Codes that indicate a service mode rather than a fault are worth recognising, because the natural assumption on seeing any code is that something is broken. Here the furnace is simply doing what it was told.

All codes for this manufacturer

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

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.