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.