Ruud UGRA-07EMAES Error Code 4 Blinks: Pressure Switch Shorted
What Does Code 4 Blinks Mean?
At the start of a cycle, before the inducer runs, the IFC checks that the pressure switch is open. A healthy switch sits open at rest and only closes once the induced draft motor proves a draft. If the board sees the switch already closed at the start, it flashes four blinks and won't proceed, because it can no longer trust the switch to verify safe venting.
On this furnace the almost-always cause is a pressure switch whose internal contacts are stuck or welded closed, so it never opens. Moisture or condensate trapped in the switch body or its hose can also hold the contacts closed. Less often, shorted or pinched wiring between the switch and the IFC makes the board read a closed circuit. Either way the fix is component-level — replacing the switch or repairing the wiring — not something to work around.
This 4-blink "stuck closed" fault is the mirror image of the 2-blink "pressure switch open" fault on the same board. With two blinks the switch never closes when it should; with four blinks it never opens when it should. Both interlocks protect against firing the burners without proven venting, which is why the manual warns against ever jumpering the switch.
What You'll Notice
- No heat; the furnace won't begin its normal startup sequence.
- The inducer may not start at all, because the board fails its pre-start switch check.
- A repeating four-blink pattern on the status LED.
- The fault appears immediately on a heat call rather than after several minutes.
- The problem persists regardless of weather or outdoor vent condition, unlike a blocked-vent 2-blink fault.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Stuck pressure switch contacts | Most common | ✗ Call a pro → |
| Shorted wiring to pressure switch | Uncommon | ✗ Call a pro → |
How This Is Diagnosed
A technician confirms the switch state at rest with the inducer off — a healthy switch reads open (no continuity). If it reads closed with no draft present, the switch is stuck and gets replaced. Before condemning the switch they inspect the switch hose and body for trapped water or condensate, since moisture can artificially hold the contacts closed, and they check the switch wiring and connector for a short, pinch, or damage that could make the board read a closed circuit.
Only after the switch is confirmed stuck and the wiring is ruled out is the switch replaced with the correct rating for this furnace. Because a stuck-closed switch defeats the venting safety interlock, the manual is explicit that it must be replaced, never bypassed or jumpered.
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 four-blink code is present (the switch or its wiring needs professional testing and replacement)
- The furnace won't start its sequence regardless of the outdoor vent condition
- Anyone has suggested jumpering or bypassing the pressure switch (do not run it that way)
- Moisture, a cracked hose, or damaged wiring is visible at the pressure switch
Frequently Asked Questions
What does 4 blinks mean on a Ruud UGRA?
The pressure switch is stuck closed when the board expects it open, so the furnace won't start. The switch almost always needs replacing.
What's the difference between 2 blinks and 4 blinks?
Two blinks means the switch won't close (often a blocked vent); four blinks means it won't open (a stuck or shorted switch). They're opposite failures of the same safety switch.
Can I bypass the pressure switch to get heat?
No. The switch verifies safe venting, and bypassing it can let the burners fire without proven exhaust flow, which is dangerous. It must be replaced, not jumpered.
How much does a pressure switch replacement cost?
The switch itself is a relatively inexpensive part, but the total depends on labor and your area, so cost varies by region.
Sources
✓ Verified against manufacturer service manual — March 2026