Goodman furnace 2 flashes: Pressure switch is closed when it should be open
Two flashes means the control checked the pressure switch before starting the draft inducer and found it already closed. The switch is supposed to be open at rest, so the control refuses to proceed.
Applies to: Goodman GMS, GMP, GMH, GMV8, GMV9 and Amana AMH, AMV9 series gas furnaces with a single red diagnostic LED. On Goodman GMSS9 and Amana AMSS9 the same flash count is described as the pressure switch circuit being closed.
What it means
The pressure switch is a safety interlock that proves the draft inducer is actually moving air before any gas is released. It works by sensing the suction the inducer creates, and it is designed to sit open when the inducer is off. Before each cycle the control verifies that it really is open — because a switch stuck closed would prove draft that does not exist, and the furnace could then fire with a blocked flue. Finding it already closed, the control stops. This is the safety system working exactly as intended, and it is one of the faults where the code is telling you something specific and useful rather than pointing at a general area.
Most common causes
- The pressure switch contacts have stuck closed and no longer open when the inducer stops.
- The switch's sensing hose is pinched, kinked, or routed so that it holds pressure.
- Water in the sensing hose or in the pressure tap, holding the switch closed.
- A short in the wiring to the switch, which looks electrically identical to closed contacts.
- The wrong pressure switch fitted during a previous repair — these are rated for a specific model and pressure and are not interchangeable.
- On two-stage models, a low-stage and high-stage switch swapped during service.
How to diagnose it
- Count the flashes carefully and confirm the pattern repeats after a pause.
- Note whether the inducer motor runs at all. On this fault it usually does not start, because the control stops before that step.
- Check whether the furnace has recently been serviced. A switch or hose disturbed during other work is a common trigger for this appearing suddenly.
- Look for condensate problems elsewhere in the system, such as a drain that has been backing up, since water reaching the sensing hose is a frequent cause on high-efficiency models.
How to fix it
- Clearing a blocked condensate drain is within reach of a confident homeowner and is worth checking, since it causes several related faults.
- The pressure switch, its hoses, and its wiring belong to a technician. The switch proves safe venting, and a furnace that runs with a defeated or bypassed pressure switch can vent combustion products, including carbon monoxide, into the house.
- Never jumper a pressure switch to get the furnace running, even briefly. It is the only thing standing between a blocked flue and a fired burner.
- Replace a failed switch with the exact part specified for the model. The pressure setpoint is model-specific and a close substitute is not a substitute.
Notes
This code and the three-flash code are opposite halves of the same test — one says the switch is closed when it should be open, the other says it will not close when it should. Miscounting between them sends the diagnosis in completely the wrong direction, so it is worth counting twice.
Related
All codes for this manufacturer
Goodman and Amana furnace fault codes — every code, with what differs between models.
Not sure this is your brand?
The same count means something else on other furnaces. What 2 flashes means on every brand puts them side by side.