Ruud UGRA-07EMAES Error Code 4 Blinks: Pressure Switch Shorted
What Does Code 4 Blinks Mean?
A 4-blink code on the Ruud UGRA-07EMAES means the pressure switch remains closed when it should be open. The pressure switch is a safety component that verifies the inducer motor is creating adequate draft to vent combustion gases outside. It should only close after the inducer starts running. When it remains closed at rest, the control board cannot trust the venting verification and will not proceed with ignition.
The primary cause is a defective pressure switch with contacts that have stuck or welded together. This is a mechanical failure that happens over time as the switch cycles thousands of times during normal operation. Moisture or water accumulating in the switch body or its connected hoses can also hold the contacts closed artificially. In rarer cases, a short in the wiring between the switch and the control board can cause the board to read the switch as closed.
This is a safety-critical repair. Do not attempt to bypass the pressure switch or force it open. A licensed HVAC technician needs to test the switch, inspect the hose connections for moisture, and replace the switch if its contacts are stuck.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Stuck pressure switch contacts | Most common | ✗ Call a pro → |
| Shorted wiring to pressure switch | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- When this code appears — the pressure switch is a safety device that must be professionally diagnosed and replaced
✓ Verified against manufacturer service manual — March 2026