Goodman furnace E9: High stage pressure switch stuck open
E9 means the second-stage pressure switch did not close when the furnace called for high fire. Low-stage heating usually still works, so the symptom is a furnace that heats but never reaches full output.
Applies to: Goodman GMVC96, GMVM97, GCVC96, GCVM97 and Amana AMVC96, AMVM97 two-stage and modulating gas furnaces with a two-character alphanumeric display. Older two-stage boards report the equivalent condition as nine flashes.
What it means
When a two-stage furnace steps up to high fire it moves more combustion air, and a separate pressure switch must close to prove that draft. E9 means it did not. The practical consequence is distinctive and easy to misread: the furnace is not dead. It runs on low fire, which in mild weather may be perfectly adequate, so the fault often goes unnoticed until it turns cold. A furnace that used to satisfy the thermostat and now runs continuously without reaching setpoint is the usual way people meet this code — and by then the underlying restriction has often been developing for weeks.
Most common causes
- The high stage pressure switch has failed and no longer closes.
- The sensing hose to the high stage switch is disconnected, kinked, or blocked.
- The inducer is not reaching high stage speed, so the switch never sees its rated pressure.
- A partly restricted vent or intake — adequate for low fire, insufficient for high fire, which is exactly why the fault appears only at second stage.
- A partly blocked condensate drain, which restricts more at the higher firing rate.
- The two pressure switches swapped during a previous repair.
- A wiring fault in the high stage switch circuit.
How to diagnose it
- Note whether the house heats slowly rather than not at all. That pattern fits this fault and rules out several others.
- Check the outside vent termination. A partial restriction is precisely what produces a high-stage-only failure.
- Check the condensate drain for slow drainage rather than complete blockage.
- Note whether the fault followed a service visit, since swapped switches are a genuine and easily missed cause.
- Confirm the furnace is two-stage or modulating; a single-stage model showing this means the code has been misread.
How to fix it
- Clear the vent termination and condensate drain if either is restricted. Both are within homeowner reach and both cause this.
- The pressure switches, hoses, and inducer are technician work.
- Have the technician confirm the switches are fitted the right way round if the furnace was recently serviced.
- Do not simply live with low fire and ignore the code. The partial restriction that causes it usually worsens, and eventually it affects low fire too.
Notes
A furnace stuck on low fire is easy to tolerate in mild weather and impossible in a cold snap. Acting when the code appears rather than when the house stops keeping up is typically several weeks and one weather change cheaper.