Rheem Furnace 3 flashes: What It Means & How to Fix It
Compiled & reviewed by the HVAC Flash Codes editorial team · Updated 2026-06-25 · confidence: high
⛔ Stop — call a licensed pro
What does Rheem furnace 3 flashes mean?
Limit switch open — the high-limit (or rollout) safety control has opened, typically from overheating or low airflow. Most often caused by Dirty/clogged air filter restricting airflow.
What your furnace LED does. The diagnostic light blinks 3 flashes, pause, repeat — that pattern is Rheem furnace 3 flashes.
What Rheem furnace 3 flashes means
Limit switch open — the high-limit (or rollout) safety control has opened, typically from overheating or low airflow.
Common causes
Dirty/clogged air filter restricting airflow
Blocked supply or return vents/registers
A blower-motor problem or closed dampers
A tripped rollout switch (flame rollout / heat-exchanger issue)
Homeowner-safe steps to try
Replace a dirty air filter and confirm it's the correct size
Open and unblock all supply registers and return grilles
Let the furnace cool, then cycle power once at the breaker
Do not reset or bypass any rollout or limit safety switch
When to call a licensed HVAC technician
If the basic checks below don't clear the code, the fault recurs, or anything involves the gas valve, burners, flame sensor or wiring, stop and book a licensed HVAC technician. Repairs to the combustion or gas system are not DIY.
⚠️ Safety first. Gas furnaces burn fuel and produce combustion gases. If you ever smell gas (a rotten-egg or sulfur odor), hear hissing, or your carbon-monoxide alarm sounds, do not touch light switches, thermostats, or the furnace — leave the home immediately and call your gas utility's emergency line or 911 from outside. Homeowners should limit themselves to simple, safe steps: setting the thermostat, checking and replacing the air filter, confirming the furnace switch and breaker are on, keeping supply registers and return grilles open, and clearing snow, ice, or debris from outdoor vent and intake terminations. Never bypass, jumper, or reset safety switches (limit, flame-rollout, or pressure switches), never open the gas valve or burner compartment, and never attempt combustion, electrical, or control-board repairs yourself. Error codes point toward a problem but are not a substitute for proper diagnosis — when in doubt, turn the system off and call a licensed HVAC technician. Keep working carbon-monoxide detectors on every level of your home.
When to call a pro: Call a licensed HVAC technician if the code persists after restoring airflow, or any time a rollout control is involved — rollout trips can indicate a dangerous heat-exchanger or combustion fault. If you smell gas, leave and call your gas utility or 911 from outside.
Rheem furnace 3 flashes FAQ
What does Rheem furnace 3 flashes mean?
Limit switch open — the high-limit (or rollout) safety control has opened, typically from overheating or low airflow.
What causes Rheem furnace 3 flashes?
Common causes: Dirty/clogged air filter restricting airflow; Blocked supply or return vents/registers; A blower-motor problem or closed dampers; A tripped rollout switch (flame rollout / heat-exchanger issue).
Can I fix Rheem furnace 3 flashes myself?
You can safely try: Replace a dirty air filter and confirm it's the correct size; Open and unblock all supply registers and return grilles; Let the furnace cool, then cycle power once at the breaker; Do not reset or bypass any rollout or limit safety switch. Call a licensed HVAC technician if the code persists after restoring airflow, or any time a rollout control is involved — rollout trips can indicate a dangerous heat-exchanger or combustion fault. If you smell gas, leave and call your gas utility or 911 from outside.
Sources: my.rheem.com · my.rheem.com. General information for homeowners, not professional advice — confirm against your furnace's manual and a licensed technician.