Rheem Furnace Error Code 45: Meaning, Causes, and Fixes

The Rheem furnace error code 45 indicates a pressure switch problem or a blocked inducer system that prevents safe ignition and operation. This article explains what Error Code 45 means, common causes, step-by-step troubleshooting, safety tips, and when to contact a professional technician. The guidance applies to most Rheem and Ruud gas furnaces and is optimized for users searching for “Rheem Furnace Error Code 45”.

Item	Quick Summary
Error Code	45
Primary Meaning	Pressure Switch Open / Inducer Airflow Issue
Common Causes	Blocked vent, faulty pressure switch, inducer motor failure, loose tubing
Immediate Actions	Power cycle, inspect vents, check condensate and tubing, reset if safe
When To Call Pro	If troubleshooting steps don’t restore operation or if gas/electrical safety concerns exist

What Error Code 45 Means

Error Code 45 on Rheem furnaces typically signifies a pressure switch or venting problem that prevents the furnace from detecting proper draft before ignition. The pressure switch is a safety device that confirms the inducer motor is creating negative pressure for exhaust. If the switch does not close when expected, the control board displays Code 45.

How The Pressure Switch System Works

The inducer motor starts first to create a draft and remove combustion gases. The pressure switch senses that draft through a small vacuum line; when the proper negative pressure is present the switch closes and allows ignition. If the switch stays open, the furnace will lock out to prevent unsafe combustion.

Common Causes Of Error Code 45

Understanding typical causes helps prioritize troubleshooting. Common causes include blocked exhaust/air intake, clogged condensate or drain lines, pinched or disconnected pressure tubing, a failing pressure switch, and a weak inducer motor.

• Blocked Venting: Outside terminals clogged with debris, bird nests, snow, or ice can prevent proper airflow.
• Clogged Condensate Drain: High-efficiency condensing units can have blocked traps or pumps that cause pressure issues.
• Damaged Tubing: The small rubber tubing between the inducer and pressure switch can be disconnected, pinched or cracked.
• Faulty Pressure Switch: Internal failure of the switch prevents it from closing even with correct vacuum.
• Inducer Motor Problems: If the inducer doesn’t reach correct RPMs the switch may not see required vacuum.

Safety First: Before Troubleshooting

Working on gas furnaces involves hazards. Turn off power to the furnace at the service switch or breaker before inspecting internal components. Do not attempt repairs beyond basic visual checks and non-invasive steps if unfamiliar with HVAC systems or gas safety.

Step-By-Step Troubleshooting Guide

1. Reset And Observe

Begin with a simple reset. Turn the furnace power off for 60 seconds and then back on. Attempt a call for heat and observe the sequence. Note the exact light code pattern or display messages for diagnostics.

2. Check Outdoor Intake/Exhaust Terminals

Inspect the furnace’s PVC or plastic intake and exhaust terminals outside the home. Remove debris, snow, ice, or nests and ensure clear airflow. For blocked vents, clearing the obstruction often resolves Code 45 quickly.

3. Inspect Pressure Tubing And Connections

Locate the small vacuum tubing from the inducer housing to the pressure switch. Check for loose fittings, pinches, or cracks. Reconnect or replace tubing if damaged. A quick test is to gently blow through the tubing with the furnace off to confirm it’s open.

4. Check Condensate And Drain Lines

High-efficiency units condense water; a clogged trap or drain can back up and affect pressure readings. Clean traps, clear standing water, ensure condensate pumps operate, and verify drains are flowing freely.

5. Observe Inducer Motor Operation

Start a heating call and listen for the inducer motor startup. If the inducer does not start, runs slowly, or makes unusual noises, it may be failing. A weak or stalled inducer often causes the pressure switch to stay open.

6. Test The Pressure Switch (For Technically Experienced Users)

If comfortable and with power on, a multimeter can test the switch continuity at appropriate times in the start cycle. The switch should be open at rest and close when the inducer reaches speed. Only attempt this if experienced with electrical diagnostics and following safety precautions.

7. Inspect For Cracked Heat Exchanger Or Blockages Inside Furnace

Internal blockages or serious mechanical issues can affect draft. Visual inspection for soot buildup, debris, or signs of combustion problems is useful. Suspected cracked heat exchangers require immediate professional evaluation due to carbon monoxide risks.

When To Call A Professional

If basic checks (vent clearing, tubing, condensate) do not fix Code 45, or if electrical components, gas valves, or heat exchanger integrity are suspected, contact a licensed HVAC technician. Technicians can safely test pressure switch operation, verify inducer amperage, and replace defective parts.

Parts Replacement And Cost Considerations

Common parts associated with Error Code 45 include pressure switches, inducer motors, condensate traps/pumps, and pressure tubing. Estimated costs vary: pressure switch parts may be modest, while inducer motor replacement can be more expensive due to parts and labor. Always get multiple estimates and verify technician licensing.

Part	Typical Issue	Estimated Cost Range (Parts+Labor)
Pressure Switch	Fails To Close	$150 – $350
Inducer Motor	Weak/Not Starting	$300 – $700
Condensate Pump/Trap	Clogged/Overflowing	$100 – $350
Vent Terminals	Blocked/Damaged	$50 – $250

Preventive Maintenance To Avoid Error Code 45

Regular maintenance reduces the chance of a pressure-related lockout. Recommended tasks include annual HVAC inspection, cleaning intake/exhaust terminals, checking condensate lines, replacing air filters every 1–3 months, and ensuring the furnace has adequate clearance around it.

• Annual Tune-Up: Professional inspection and cleaning of inducer motor, burners, and vent system.
• Filter Maintenance: Replace filters to maintain airflow and reduce strain on the system.
• Keep Vents Clear: Remove debris, snow, or vegetation near outdoor terminals.
• Check Condensate: Ensure traps, pumps, and drains are clean and working.

Diagnostic Tips For Technicians

Technicians use gauges and manometers to measure vacuum across the pressure switch and compare to manufacturer specifications. Observing inducer motor amperage and RPM, testing pressure switch continuity under load, and inspecting control board error logs help pinpoint root causes efficiently.

Common Misdiagnoses And Pitfalls

Replacing the pressure switch without addressing the underlying inducer or vent problem often leads to repeated failures. Likewise, ignoring condensate or vent obstructions and only swapping electrical parts can result in recurring Code 45 events.

Compatibility And Models Affected

Error Code 45 is common across many Rheem and Ruud models that use a pressure switch safety system, especially mid-efficiency and high-efficiency gas furnaces. Always consult the specific model’s installation and service manual for exact diagnostic steps and pressure specifications.

Frequently Asked Questions

Can A Furnace Run With Error Code 45?

No. Error Code 45 is a safety lockout. The furnace will not complete its ignition sequence until the pressure switch confirms proper draft.

Is Error Code 45 Dangerous?

The code itself indicates a safety system working correctly to prevent dangerous combustion. The underlying cause may present hazards if it involves a cracked heat exchanger or blocked exhaust; schedule professional service if in doubt.

Can A Homeowner Replace The Pressure Switch?

Technically possible for experienced DIYers, but it involves electrical work and gas system safety. Professional replacement ensures proper calibration and diagnosis of root causes.

How Long Will Troubleshooting Take?

Simple fixes like clearing vents or reconnecting tubing can take under an hour. Comprehensive diagnostics, parts ordering, or inducer replacement may take several hours to a day depending on part availability.

Useful Links And Resources

Refer to the furnace’s model-specific service manual for exact error code definitions and pressure readings. Homeowners can also consult manufacturer support pages and EPA/ASHRAE resources for gas appliance safety guidance.

Key Takeaways

Error Code 45 Signals A Pressure/Inducer Issue. Start with safe, simple checks—vent clearance, condensate, and pressure tubing. If basic steps fail or if gas/electrical concerns arise, contact a licensed HVAC technician for in-depth diagnostics and repair. Regular maintenance is the best prevention against recurring Code 45 events.