Goodman GMVM970803BN Error Code E8: High Stage Pressure Switch Stuck Closed

What Does Code E8 Mean?

An E8 code on the Goodman GMVM970803BN indicates the high stage pressure switch is stuck in the closed position before the heating cycle begins. Because this is a modulating, variable-speed furnace, Goodman fits it with two separate pressure switches — a low stage switch and a high stage switch — so the Integrated Control Module can confirm safe venting at each firing rate independently. Before a cycle starts, the control module expects both switches to be open (their default, unpressurized state). When it finds the high stage switch already closed, it cannot trust that switch to verify venting for high-fire operation, so it blocks high stage.

This is the high-stage counterpart of the E1 code, which reports the low stage pressure switch stuck closed. The difference matters: E1 stops the furnace from operating at all, but E8 is far less disruptive because the low stage circuit is still trustworthy. The Integrated Control Module simply keeps the burner and inducer at their low-fire settings and continues to deliver heat, which is why this model rates E8 as a low-severity fault rather than a hard lockout. It is essentially a degraded-mode condition rather than a no-heat condition.

The usual cause is the high stage switch contacts sticking or welding closed, or an electrical short in the wiring between that switch and the control module that makes the circuit read closed even when the diaphragm is open. Because the control module also drives the ECM communicating blower to match each firing rate, a furnace locked into low stage will run the blower at its lower low-stage airflow as well. E8 should not be confused with E9, which reports the high stage switch failing to close (stuck open) once the inducer is running; E8 is the opposite pre-start condition.

What You'll Notice

• The furnace still produces heat, but it never ramps up to full output — it runs only at its lower, quieter low-fire setting
• The home heats slowly or cannot keep up on the coldest days when full capacity would normally be needed
• Heating cycles run noticeably longer than usual because the furnace cannot reach high fire
• The dual 7-segment display on the control board shows E8
• The blower runs at a lower, steadier airflow than it does during normal high-stage heating

Common Causes

How This Is Diagnosed

A technician first confirms the furnace is actually locked into low stage and reads the stored fault history on the control module's diagnostics menu to see how often E8 has repeated. With power removed, they test the high stage pressure switch with a multimeter, checking whether its contacts read closed while the diaphragm is at rest — a switch that is closed with no negative pressure applied is faulty. They also back-probe the switch wiring to the Integrated Control Module to rule out a short that could make an open switch read as closed.

Because E8 and E9 share the same high stage switch, the technician verifies which failure mode is present before condemning the part: E8 is a switch stuck closed at rest, while E9 is a switch that will not close under draft. If the contacts are stuck, the switch is replaced with the exact model-specific part so the factory set point is preserved; substituting an incorrect switch can defeat the venting safety check.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• The furnace only ever runs on low heat and will not step up to full capacity, and the display shows E8
• E8 returns after power is cycled, pointing to the high stage switch or its wiring rather than a transient glitch
• The home cannot reach the thermostat setpoint during very cold weather because high stage is unavailable
• The high stage pressure switch needs replacement with the correct part matched to the original set point

✓ Verified against manufacturer service manual — March 2026