Ruud U802VA050317MSA Error Code *T055_F: Inducer Hi Pressure Switch Won't Open (Two-Stage Only)

What Does Code *T055_F Mean?

Fault code T055_F on the Ruud U802VA applies only to two-stage models — the asterisk shown in Ruud's documentation (*T055_F) marks it as a two-stage-only fault. It is set when the high-stage inducer pressure switch fails to OPEN when the IFC expects it to, and the T (transient) prefix means the board saw this intermittently rather than as a constant condition.

A two-stage furnace has a separate high-stage pressure switch in addition to the low-stage switch. This high-stage switch proves the stronger draft that the inducer produces when the furnace fires on high heat. Its contacts should be open when high-stage draft is not present and should only close once the inducer builds the higher pressure. When the board checks and finds the high-stage switch still closed at a point where it should be open, it cannot confirm the switch is tracking pressure correctly and logs the fault.

Because this fault is transient, the switch is not stuck closed continuously — it may be sticking occasionally, or moisture and debris in its sensing hose may be trapping pressure now and then. The persistent version of the same problem is reported as its active counterpart when the high-stage switch stays closed continuously. This transient code is often the earlier warning that the same high-stage switch is beginning to fail.

On the U802VA, the control will not run a heat cycle during a lockout condition, and lockouts can be cleared by cycling power. Since the fault is specific to the high-stage switch, low-stage (low-heat) operation may still work even when high-stage proving is intermittently faulting.

What You'll Notice

• The furnace heats inconsistently, sometimes running on low heat but stumbling when it should step up to high fire
• Occasional failed or delayed heat cycles that then recover on a later attempt
• The furnace may seem to run normally much of the time, since the fault is intermittent
• The contractor app logs the *T055_F transient high-stage pressure switch fault
• Symptoms show up more on the coldest days when the furnace calls for high-stage heat most often

Common Causes

How This Is Diagnosed

A technician confirms this is a two-stage model and focuses on the high-stage pressure switch circuit specifically, separating it from the low-stage switch. They check the high-stage switch's state and continuity at rest, looking for a switch that reads closed when it should be open, and inspect its dedicated sensing hose and port for moisture, condensate, or debris that could trap pressure and cause intermittent sticking.

Because the fault is transient, the technician typically reviews the fault history in the app to gauge how often it recurs and watches a high-fire cycle to see the switch behavior in real time. If the hose is clear but the high-stage switch sticks closed intermittently, the switch is replaced with the correct part for this two-stage model and verified through several high-stage cycles.

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 *T055_F code appears on a two-stage U802VA, indicating the high-stage pressure switch is intermittently failing to open
• The furnace runs on low heat but has trouble stepping up to high fire
• The high-stage sensing hose shows moisture, condensate, or debris
• The transient fault recurs and is becoming more frequent, suggesting a switch beginning to fail

✓ Verified against manufacturer service manual — March 2026