Ruud U802VA050317MSA Error Code *A055_F: Inducer Hi Pressure Switch Won't Open (Two-Stage Only)
What Does Code *A055_F Mean?
Fault code A055_F on the Ruud U802VA applies only to two-stage models — Ruud's documentation marks it *A055_F for two-stage-only. It is set when the high-stage inducer pressure switch fails to OPEN when the IFC expects it to, and the A (active) prefix means this is a persistent, currently-present condition rather than an occasional one.
A two-stage furnace uses a separate high-stage pressure switch to prove the stronger exhaust draft created when the inducer runs for high-fire heating. That switch should be open when high-stage draft is not present and should only close under the higher inducer pressure. When the board finds the high-stage switch continuously closed at a point where it should be open, it cannot verify that the switch is tracking pressure correctly, so it faults and will not run the affected cycle.
A055_F is the persistent counterpart to the transient high-stage won't-open fault: the transient version is set when the board sees the problem intermittently, while A055_F is set when the switch stays closed consistently. Reaching the active code usually indicates the high-stage switch has failed mechanically — a contact set that is welded or stuck, or a diaphragm no longer returning to its rest position — rather than a passing disturbance like wind or a trace of moisture.
On the U802VA, lockouts can be cleared by cycling power, but that only clears the attempt — it does not fix the switch. Because the fault is specific to the high-stage switch, the furnace may still be able to provide low-stage (low-heat) operation, but full two-stage performance is unavailable until the switch is replaced.
What You'll Notice
- The furnace will not run on high fire and, at most, delivers only low-heat output
- The home warms slowly or fails to reach setpoint on the coldest days when high-stage heat is needed
- Heat cycles for the high-stage call fail or are blocked, and the condition does not clear on its own
- The contractor app reports the *A055_F active high-stage pressure switch fault
- Cycling power may temporarily allow a retry, but the fault returns
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Failed high-stage pressure switch | Most common | ✗ Call a pro → |
How This Is Diagnosed
A technician verifies the model is two-stage and isolates the high-stage pressure switch circuit from the low-stage switch. With the system at rest they check the high-stage switch state and continuity, confirming it is stuck closed when it should read open, and inspect the dedicated high-stage sensing hose and port for any moisture or debris that could hold pressure.
Because A055_F is persistent, the technician expects to find a switch that will not open under normal conditions rather than an intermittent event. Once the hose is ruled out and the switch is confirmed failed, it is replaced with the correct high-stage part for this two-stage model, and the technician runs several full high-fire cycles to confirm the switch now opens and closes at the proper set points.
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 *A055_F code is present on a two-stage U802VA and high-fire heating is unavailable
- The furnace only manages low heat and cannot reach setpoint on very cold days
- Cycling power clears the lockout attempt but the fault returns, indicating a failed switch rather than a passing disturbance
- The high-stage sensing hose shows moisture or debris that may be holding the switch closed
Frequently Asked Questions
Is A055_F worse than T055_F on my two-stage Ruud U802VA?
They describe the same high-stage won't-open problem, but A055_F is the active, persistent version while T055_F is the intermittent one. A055_F generally means the high-stage switch has failed and needs replacement, rather than just occasionally sticking.
Can my furnace still heat with A055_F?
Because the fault is on the high-stage switch, the furnace may still run on low heat, but it cannot deliver full high-fire output. On the coldest days that may not be enough, so have the high-stage pressure switch replaced by a technician.
Why do only two-stage U802VA models get this code?
Only two-stage models have a separate high-stage pressure switch to prove the stronger high-fire draft. Single-stage furnaces lack that second switch, so this high-stage fault does not apply to them.
✓ Verified against manufacturer service manual — March 2026