E9
High-stage pressure-switch circuit is not closed; furnace operates in low stage only
This code typically points to
- Pressure-switch hose blocked/pinched/improperly connected
- Blocked flue/inlet air pipe
- Blocked drain
- Weak induced-draft blower
- Incorrect pressure-switch set point or malfunctioning contacts
- Loose/improper wiring
Next checks to confirm
- Inspect hose and venting/intake/drain
- Verify induced-draft performance
- Correct pressure-switch set point/contact issue
- Tighten/correct wiring
Escalation
Furnace fails to operate on high stage and remains in low stage only
Reset behavior
Clears after high-stage pressure-switch proving is restored.
Service Soon
Schedule repair