Troubleshooting Rheem Error Code 55: What It Means & How to Fix

While a cold house and a non-responsive furnace are frustrating, this error is a logic-based safety lockout. As a senior engineer, I can assure you that this is one of the more diagnostic-friendly codes. With a systematic approach to the electrical and pneumatic components of your Rheem unit, we can identify the failure point—whether it’s a welded contact, a logic error, or a simple blockage—and restore your heating system to peak performance.

Symptoms of Rheem Error 55

When a Rheem furnace encounters Error 55, the behavior of the unit deviates significantly from its standard firing sequence. You will likely observe the following physical and mechanical signs:

• The Diagnostic LED Flash: On the integrated furnace control (IFC) board, you will see a “55” code displayed on the dual seven-segment display, or a sequence of five amber/yellow flashes followed by five more, depending on your specific model’s age.
• Inducer Inactivity: In many logic configurations, the draft inducer motor may not even attempt to spin up. Because the board detects the pressure switch is already closed, it refuses to energize the motor to prevent potential combustion issues.
• Cold Air Circulation: If the blower motor was already running from a previous cycle, it may continue to blow unheated, ambient-temperature air throughout the ductwork while the burners remain extinguished.
• Lack of Ignition: You will notice the absence of the typical “clicking” of the spark igniter or the orange glow of the Hot Surface Igniter (HSI). The gas valve will remain closed as a primary safety precaution.

Why is my Rheem showing Error 55?

To resolve this error, we must understand the engineering behind the fault. The pressure switch is a diaphragm-operated Single Pole Single Throw (SPST) switch designed to prove that the inducer motor is creating enough negative pressure to safely exhaust flue gases. If it is “Stuck Closed,” the system is compromised.

• Internal Mechanical Diaphragm Failure: Over years of operation, the rubber diaphragm inside the switch can become brittle or lose its elasticity. If the diaphragm gets physically “stuck” in the collapsed position due to heat fatigue or material degradation, the internal contacts remain fused together even when the vacuum pressure is zero.
• Moisture and Siphonage Issues: In high-efficiency (90%+) condensing furnaces, moisture is a byproduct of combustion. If the furnace is not pitched correctly or if the condensate drain lines are partially blocked, water can back up into the pressure switch tubing. This water can create a “slug” that holds the diaphragm closed through capillary action and surface tension, even after the motor stops.
• Electrical Contact Welding: Though rare, a voltage spike or excessive arcing across the small switch contacts can “weld” them shut. This creates a permanent electrical path. If the control board sends a sensing voltage and receives it back immediately before the inducer starts, it triggers Error 55.
• Control Board Logic Fault: Occasionally, the issue isn’t the switch at all, but a “ghost” reading on the Integrated Furnace Control (IFC). If a relay on the board has failed in a closed state, the board might misinterpret its own internal circuit state as a closed pressure switch.

Comprehensive Repair Guide

Follow these steps in order. As a safety professional, I must insist that you disconnect the 120V power supply to the furnace before removing any panels or touching internal wiring.

1. Isolate and Identify: Remove the upper access panel of your Rheem furnace using your 1/4″ nut driver. Locate the pressure switch—it is typically a small, circular plastic component with one or two translucent rubber hoses attached to it. It will have two wires (usually orange or yellow) connected to spade terminals.
2. Check for “Stuck” Continuity: This is the definitive test. Disconnect the two wires from the pressure switch terminals. Set your digital multimeter to the Ohms (Ω) or Continuity setting. Place your probes on the two terminals of the switch while the furnace is OFF.
   
   Warning: If your meter shows “0.0” or beeps, the switch is definitively stuck closed and must be replaced. A healthy switch should show “O.L” (Open Loop) when the furnace is off.
3. Inspect the Pneumatic Lines: Remove the rubber tubing from both the switch and the inducer housing. Inspect the inside of the tubes for water droplets or debris. Blow through the tubes to ensure they are clear. If you find water, you must investigate your condensate drain system for clogs, as this is the root cause of the switch sticking.
4. Clear the Inducer Port: Use a thin wire or a straightened paperclip to gently poke into the small plastic “nipple” on the inducer motor housing where the hose connects. Carbon buildup or “wasp nests” (in summer-to-winter transitions) can create a vacuum seal that holds the switch closed. Ensure this port is perfectly clear.
5. The “Tap” Test (Temporary Measure): Sometimes a diaphragm is simply caught. With the wires disconnected, gently tap the side of the pressure switch with the handle of a screwdriver. Re-test for continuity. If the circuit opens (shows O.L), the switch was mechanically stuck. While this might get you heat tonight, it indicates an aging diaphragm that requires replacement immediately.
6. Replace the Switch: If the switch fails the continuity test (stays closed with no vacuum), unscrew the mounting bracket and install a genuine Rheem replacement part. Ensure the pressure rating (measured in inches of Water Column, e.g., -0.50″ W.C.) matches the original exactly.
7. System Reset: Reconnect all wires and hoses. Reinstall the furnace doors (the door switch must be depressed for the unit to power up). Restore power and set the thermostat to “Heat.” The furnace should now clear the 55 code, start the inducer motor, and proceed to ignition.

How to Prevent Error 55

Preventative maintenance is the difference between a reliable system and an emergency repair call in the middle of a blizzard. To keep your pressure switches functioning, focus on these three engineering-driven tips:

• Leveling and Pitch: Ensure your furnace is slightly pitched forward (per manufacturer specs, usually 1/4″ to 1/2″) toward the condensate drain. This prevents water from pooling in the inducer housing, which is the leading cause of pressure switch “slugging” and premature diaphragm failure.
• Annual Port Cleaning: During your yearly inspection, don’t just change the filter. Use a small vacuum or compressed air to clean the inducer motor’s cooling fan and the pressure ports. Removing dust prevents the ports from becoming restricted, which maintains the proper pressure differential required to snap the switch open and closed cleanly.
• Power Quality Management: Because the furnace control board is sensitive to voltage fluctuations that can “weld” switch contacts or damage board relays, install a dedicated HVAC surge protector. This protects the delicate SPST switches and the IFC from electrical “noise” that leads to Error 55 logic faults.

FAQ

Frequently Asked Questions

Q: Can I just jump the wires together to bypass Error 55?
A: Absolutely not. This is a critical safety hazard. If you jump the wires, you are telling the furnace that there is proper exhaust flow when there might not be. This can lead to the buildup of Carbon Monoxide (CO) in your home or a fire hazard. The control board is designed to detect this bypass, which is exactly why Error 55 exists (to stop the furnace if it thinks someone has bypassed the switch or if the switch has failed in the “on” position).

Q: Is Error 55 the same as Error 57?
A: No. While both involve the pressure switch, Error 57 usually means the switch is “Stuck Open.” This means the inducer is running, but the switch won’t close. Error 55 is the opposite: the switch is “Stuck Closed” when it should be open. They require different diagnostic steps.

Q: Will a dirty air filter cause Error 55?
A: Generally, no. Airflow issues related to dirty filters usually trigger “Limit Switch” errors (like Error 33). Error 55 is strictly related to the combustion air/exhaust side of the system (the inducer and pressure switch), not the indoor blower air.