Rheem 90 Plus Furnace Troubleshooting Guide

The Rheem 90 Plus Furnace Troubleshooting Guide helps homeowners diagnose and fix common problems with Rheem 90 Plus gas furnaces, covering error codes, LED blink patterns, airflow issues, ignition failures, maintenance tips, and when to call a professional. Focus is on practical, safe steps that reduce downtime and prevent expensive repairs.

Symptom	Likely Cause	Quick Action
No Heat	Thermostat, ignition, gas supply	Check thermostat, power, gas valve
Short Cycling	Overheating, airflow restriction	Clean filter, check vents
Blower Runs Constantly	Fan setting, control board	Check thermostat fan setting
LED Blink Codes	Specific component fault	Interpret LED pattern, consult manual

How Rheem 90 Plus Furnaces Work

The Rheem 90 Plus is a high-efficiency condensing gas furnace that uses electronic ignition, sealed combustion, and a secondary heat exchanger to extract more heat from fuel. Key components include the thermostat, control board, inducer motor, gas valve, hot surface igniter or intermittent pilot system, flame sensor, primary and secondary heat exchangers, and the blower assembly.

Common Symptoms And Initial Safety Checks

When a Rheem 90 Plus furnace shows problems, start with basic safety checks before diagnosing components. Safety first: shut power off at the breaker and turn off gas if a leak is suspected.

Initial Safety Checklist

• Verify thermostat settings (heat mode, setpoint higher than room temperature).
• Check the furnace switch and circuit breaker for power interruptions.
• Ensure the gas supply is turned on and nearby appliances have gas.
• Look for error LED blink codes on the control board; record the pattern.
• Smell for gas; if detected, evacuate and call the gas utility or emergency services.

Interpreting LED Blink Codes And Status Lights

Rheem furnaces use LED blink codes to indicate faults. Accurately recording blink sequences is essential for targeted troubleshooting. A typical pattern is a repeating series of blinks followed by a pause.

Common Blink Codes And Meanings

• 1 Blink: System powering up or normal operation.
• 2 Blinks: Pressure switch stuck open or inducer issue.
• 3 Blinks: Pressure switch stuck closed or shorted circuit.
• 4 Blinks: High-limit or rollout switch open (overheat condition).
• 5 Blinks: Ignition failure or flame failure.
• 6 Blinks: Flame sense failure or intermittent flame detection.
• 7 Blinks: Open flame roll-out or blocked venting.

Reference the furnace manual for exact codes; some models vary. Documenting the exact timing and number of blinks helps technicians diagnose faults more quickly.

Thermostat And Control Checks

Many “no heat” reports trace back to thermostat or control issues. Start simple with accurate temperature settings and power to the thermostat.

Thermostat Troubleshooting Steps

1. Confirm thermostat is set to Heat and the setpoint is above room temperature.
2. Replace thermostat batteries if applicable.
3. Temporarily bypass the thermostat by jumping R to W at the furnace control board to force heat call; if the furnace runs, replace or rewire the thermostat.
4. Verify wiring is secure and undamaged; corrosion or loose wires cause intermittent operation.

Power And Fuse Issues

Loss of control power or blown fuses causes furnaces to stop functioning. Inspect the 24V transformer fuse and line voltage supply.

Power Diagnosis

• Check main breaker and furnace power switch.
• Open access panel and inspect the 3A or 5A control board fuse; replace with identical type if blown.
• Measure 24VAC between R and C with a multimeter; 20–30 VAC indicates a healthy transformer.

Ignition And Flame Detection Problems

Ignition failure is a leading cause of heat loss in high-efficiency furnaces. Rheem 90 Plus models typically use hot surface igniters or intermittent pilots and rely on a flame sensor to confirm combustion.

Hot Surface Igniter Checks

• Inspect the igniter for cracks or visible damage; a fragile ceramic element often fails with age.
• Test continuity with a multimeter; a burned igniter usually reads open circuit.
• Handle igniters carefully; oils from skin shorten lifespan—use gloves.

Flame Sensor Cleaning And Testing

• Remove the flame sensor and gently clean with fine sandpaper or emery cloth to remove carbon build-up.
• Reinstall and test operation; persistent flame failure after cleaning suggests sensor replacement or grounding issues.
• Check electrode gap and positioning relative to the flame; improper alignment can prevent proper sensing.

Inducer Motor And Pressure Switch Troubleshooting

The inducer motor creates the necessary draft for combustion and works with the pressure switch to verify proper venting. Problems in this circuit trigger codes and shutdowns.

Inducer Motor Steps

• Listen for inducer operation during startup; no noise suggests motor failure or lack of 120V power.
• Measure voltage to the inducer motor; if present but motor doesn’t run, replace the motor assembly.
• Inspect for blocked intake/ exhaust vents or animal nests that restrict airflow.

Pressure Switch Steps

• Ensure hose connections to the pressure switch are intact and unobstructed.
• Test switch continuity during inducer operation; the switch should close when proper draft is established.
• Replace the pressure switch if it fails to operate despite clear venting and a running inducer.

Airflow, Filters And Ductwork Issues

Restricted airflow causes overheating and short cycling, reducing efficiency and life span. Maintaining correct airflow prevents many operational problems.

Airflow Maintenance

• Replace or clean filters every 1–3 months depending on usage and filter type.
• Inspect return and supply vents for blockages and closed dampers.
• Check blower wheel for dust accumulation and clean as necessary to maintain static pressure.
• Ensure proper duct sizing and no large disconnected sections causing pressure loss.

Heat Exchanger And Overheat Protection

The primary and secondary heat exchangers should be checked if there are unusual smells, soot, or persistent overheating. Do not attempt extensive heat exchanger repairs at home.

Signs Of Heat Exchanger Issues

• Persistent rust, cracks, or visible corrosion.
• Carbon monoxide detector alarms correlated with furnace operation.
• Black soot near burners or unusual odors.

If any of these are present, shut the furnace down and schedule an immediate professional inspection. Heat exchanger failure is a serious safety issue.

Condensate Drain And Secondary Heat Exchanger Care

High-efficiency furnaces like the Rheem 90 Plus produce condensate that must drain properly. A clogged condensate line can trigger shutdowns and cause water damage.

Condensate Troubleshooting

• Inspect the condensate trap and drain line for blockages or frozen lines in cold climates.
• Clear lines with warm water and check the condensate pump if used.
• Ensure the condensate neutralizer (if installed) is maintained to prevent buildup and odors.

Common Replacement Parts And Costs

Knowing typical replacement parts helps budget repairs. Costs vary by region and HVAC contractor but the following are common ballpark ranges.

Part	Typical Cost Range (Parts Only)
Igniter	$30 – $120
Flame Sensor	$15 – $60
Inducer Motor	$120 – $350
Pressure Switch	$25 – $100
Control Board	$150 – $500

Labor can add significantly to these parts costs depending on diagnostic time and complexity. Request written estimates and parts warranties.

Routine Preventive Maintenance Tasks

Preventive maintenance reduces emergency repairs and keeps the Rheem 90 Plus operating efficiently. Annual professional tune-ups are recommended.

• Replace filters frequently and use the correct MERV rating for the system.
• Schedule annual inspection including combustion analysis, gas pressure check, and heat exchanger visual.
• Lubricate motors if applicable and clean blower wheel and motor compartment.
• Verify venting integrity and clear any outdoor blockages.

Troubleshooting Flow Chart For Common Faults

A logical step-by-step approach helps isolate problems quickly.

1. Confirm thermostat call for heat and power to furnace.
2. Check LED blink codes and document pattern.
3. Verify inducer motor operation and pressure switch closure.
4. If inducer runs but no ignition, inspect igniter and flame sensor.
5. If furnace starts and then shuts off, inspect airflow, filters, and limit switches.
6. If suspecting heat exchanger or gas leak, stop operation and contact a professional.

When To Call A Professional

Some issues require licensed HVAC technicians or gas service professionals. Call a professional when there are gas odors, heat exchanger concerns, carbon monoxide alarms, or complex electrical and control board failures.

• Unexplained carbon monoxide detector activation.
• Cracked or corroded heat exchanger.
• Persistent ignition or flame sensing failures after home-level checks.
• Control board faults or repeated blown fuses.

Warranty, Documentation, And Replacement Considerations

Check the furnace serial plate and registration for warranty eligibility before performing repairs. Rheem often offers limited warranties on heat exchangers and parts; extended warranties may be available from dealers.

• Keep service records and receipts to support warranty claims.
• When replacing major components, compare OEM parts versus aftermarket options for compatibility.
• Consider replacement if the furnace has frequent breakdowns, rising repair costs, or efficiency loss compared to modern high-efficiency models.

Useful Tools And Multimeter Tests

Several basic tools help in home diagnostics: a multimeter, thermometer, small mirror, flashlight, nut drivers, and a narrow brush. Proper measurement techniques reduce misdiagnosis.

Key Multimeter Checks

• Measure 24VAC between R and C to verify transformer output.
• Check continuity of the igniter or flame sensor when removed.
• Measure line voltage to inducer motor and blower during operation.

Resources And Further Reading

Owner manuals, Rheem technical service bulletins, and HVAC forums provide model-specific guidance and OEM replacement part numbers. Always cross-reference manual procedures with the model plate data.

Manufacturer resources include the Rheem website, official service manuals, and certified dealer networks. Local utility conservation programs may offer rebates for high-efficiency equipment replacement.

Final Troubleshooting Tips And Best Practices

Document findings, take photos of wiring and component locations before disassembly, and replace one component at a time to isolate effects. Safety and correct diagnostics avoid unnecessary part replacement and extended downtime.

• Keep carbon monoxide detectors operational near living spaces and furnace areas.
• Schedule professional inspection annually, ideally before the heating season.
• Use OEM parts for critical safety components such as heat exchangers and control boards.