Quick Answer:
Rheem furnaces use diagnostic lights or digital displays to communicate system problems. Older models flash LED “blink codes,” while newer Rheem Prestige® and Endeavor™ systems show numeric error codes. These codes identify issues like ignition failure, airflow restrictions, or pressure switch faults so technicians can diagnose problems accurately.
Why Rheem Furnaces Use Diagnostic Fault Codes
Quick Answer:
Modern furnaces include diagnostic systems that detect safety or performance issues. When a problem occurs, the furnace shuts down and displays an error code to prevent damage or unsafe operation.
If you’re standing in a basement in Steubenville, Ohio, or Weirton, West Virginia, staring at a flashing light on your furnace, the system is trying to communicate with you.
Rheem furnaces are designed with PlusOne™ Diagnostics, which shut the furnace down before a small issue turns into:
- a cracked heat exchanger
- a dangerous combustion problem
- expensive component failure
In my 30 years working on heating systems across the Upper Ohio Valley, Rheem furnaces have proven to be some of the most reliable units in the industry.
They are also very vocal when something goes wrong.
At Honest Fix Heating, Cooling & Plumbing, we diagnose these systems as a Rheem Pro Partner and Authorized Rheem Service Provider, using manufacturer diagnostic procedures rather than guesswork.
You can verify model efficiency and heating capacity through the Air‑Conditioning, Heating, and Refrigeration Institute equipment directory:
How to Read Rheem Furnace Diagnostic Codes
Quick Answer:
Rheem furnaces display error information using either blinking LEDs or a digital two‑digit display. Identifying which system your furnace uses is the first step in diagnosing the problem.
Rheem furnaces communicate faults using two main systems.
Diagnostic Display Types
| System Type | Description |
|---|---|
| LED Blink Codes | Older units use flashing lights to indicate faults |
| Numeric Displays | Newer systems show two‑digit diagnostic codes |
Older models like Criterion II and Classic 90 Plus rely on blinking lights.
Modern models such as the Prestige® and Endeavor™ series use digital displays.
Important Diagnostic Tip
Many furnaces include a door safety switch.
When the panel is removed, the switch cuts power to the system and clears the code.
Technicians hold this switch closed while observing the furnace startup sequence.
Rheem Numeric Fault Code Reference (Modern Systems)
Quick Answer:
Newer Rheem furnaces display two‑digit diagnostic codes on a digital control board. Each code identifies a specific operating condition or safety shutdown.
These codes are common on models like:
- R98MV
- R97MV
- R962V
Rheem Numeric Fault Code Table
| Code | Meaning | Possible Cause | Homeowner Action |
|---|---|---|---|
| 0 | Standby | Furnace waiting for thermostat | Normal operation |
| H | Heating | Furnace actively heating | Normal operation |
| 10 | Ignition Lockout | Multiple failed ignition attempts | Reset power |
| 11 | Failed Ignition | Burners failed to ignite | Check gas supply |
| 12 | Low Flame Sense | Weak flame signal | Clean flame sensor |
| 13 | Flame Lost | Flame extinguished during cycle | Inspect venting |
| 14 | Unexpected Flame | Flame detected when valve closed | Shut off gas |
| 22 | Limit Switch Open | Furnace overheating | Replace air filter |
| 26 | Reversed Polarity | Electrical wiring incorrect | Call technician |
| 33 | Rollout Switch Open | Flames outside burner chamber | Professional inspection |
| 45 | Low Pressure Open | Intake restriction | Clear intake pipe |
| 57 | High Pressure Open | Exhaust restriction | Check vent outlet |
| 61 | Blower Fault | Blower motor not operating | Motor or capacitor issue |
| 93 | Control Board Failure | Internal electronic failure | Replace control board |
Rheem LED Blink Codes (Legacy Furnaces)
Quick Answer:
Older Rheem furnaces display fault codes through flashing LED lights. The number of flashes between pauses indicates the type of malfunction.
These codes apply to many Rheem models installed between 1995 and 2018.
Rheem Blink Code Guide
| Flashes | Meaning | Common Cause |
|---|---|---|
| Steady light | Normal operation | System heating normally |
| 1 Flash | Ignition failure | Dirty flame sensor |
| 2 Flashes | Pressure switch stuck closed | Faulty pressure switch |
| 3 Flashes | Pressure switch open | Vent blockage |
| 4 Flashes | Limit switch open | Dirty air filter |
| 5 Flashes | Twinning fault | Control board communication issue |
| 6 Flashes | Rollout switch open | Burner or heat exchanger issue |
The four‑flash limit switch code is extremely common across homes in the Ohio Valley.
In most cases, the cause is simply a clogged air filter restricting airflow.
Furnace maintenance guidance from the U.S. Department of Energy:
https://www.energy.gov/energysaver/furnaces-and-boilers
The Three Most Common Rheem Furnace Failures
Quick Answer:
Three issues account for a large percentage of furnace service calls: dirty flame sensors, blocked pressure switch tubing, and failed blower capacitors.
Over decades of service work, a few patterns show up repeatedly.
The Classic 90 Plus “S‑Hose” Pressure Problem
Condensing furnaces sometimes route pressure tubing in an “S” shape.
Moisture can collect in the low point of the tubing.
This blocks the pressure signal and prevents the furnace from starting.
The fix involves adjusting the tubing so condensation drains correctly.
Criterion II Flame Sensor Oxidation
Criterion II furnaces often develop carbon buildup on the flame sensor.
This reduces the electrical signal used to confirm burner operation.
The furnace expects a signal around:
2.0 microamps
Cleaning the sensor typically restores normal operation.
Blower Capacitor Failure
Many homeowners are told their blower motor has failed.
However, the real issue is often a failed run capacitor.
Common Symptom
- blower motor hums
- air does not move
- furnace overheats and trips limit switch
Replacing the capacitor often solves the issue.
Safety Warning: Rollout and Carbon Monoxide Risks
Quick Answer:
Rollout switch faults indicate dangerous combustion conditions where flames escape the burner chamber. These issues require immediate professional inspection.
Codes such as 33 or six flashes indicate a tripped rollout switch.
This can happen when:
- burners are misaligned
- venting is blocked
- the heat exchanger is cracked
Carbon monoxide safety guidance from the Consumer Product Safety Commission:
Never bypass or reset a rollout switch without identifying the cause.
Rheem Furnace Fault Code FAQs
Why is my Rheem furnace flashing a green light?
Quick Answer:
A blinking green light usually indicates the control board has power and is operating normally. If the light flashes in a specific pattern, the number of flashes corresponds to a diagnostic fault code.
Consult the furnace diagnostic chart to determine the meaning.
How do I reset a Rheem furnace fault code?
Quick Answer:
Most furnace codes reset by turning the furnace power switch off for about 30 seconds and turning it back on.
However, safety codes like rollout faults require manual reset switches and professional inspection.
Why is my furnace blowing air but not heating?
Quick Answer:
This usually indicates an ignition lockout or failed ignition sequence. The blower may run to cool the furnace while the burners remain off.
Common causes include:
- dirty flame sensor
- faulty ignitor
- gas supply interruption
What does Rheem code 22 mean?
Quick Answer:
Code 22 indicates the furnace limit switch has opened due to overheating. The most common cause is restricted airflow from a dirty air filter.
Replacing the filter usually resolves the issue.
What guarantees do you offer?
Quick Answer:
Honest Fix protects homeowners with two major guarantee programs. New installations include a 15‑year labor warranty, while repairs include a 5‑year labor warranty, backed by written service guarantees.
Lifetime Trust Shield — Installations
Installation protection includes:
- 15‑year labor warranty on HVAC installations
- 90‑day money‑back satisfaction guarantee
- no‑lemon replacement protection
- energy savings guarantee
Coverage requires annual maintenance.
Service Trust Guardian — Repairs
Repair coverage includes:
- 5‑year labor warranty on qualifying repairs
- 60‑day money‑back service guarantee
- no overtime charges for emergency service
- on‑time arrival guarantee
These protections reduce repeat repair risks.
Need Help Diagnosing a Rheem Furnace Fault Code?
At Honest Fix, we believe diagnostics should be based on measurement and evidence, not guessing.
As a Rheem Pro Partner and Authorized Rheem Service Provider, our technicians use professional diagnostic tools to identify the root cause of furnace shutdowns.
Whether you live in Steubenville, Weirton, Wintersville, Mingo Junction, or Follansbee, we provide:
- free exact quotes
- professional fault code diagnostics
- airflow and combustion testing
Experiencing a furnace fault code right now?
Contact Honest Fix today for a professional diagnosis.
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