What does Rheem Furnace Blowing Cold Air - Causes & Fix mean?

Most often the thermostat fan is set to ON instead of AUTO, running the blower constantly with no heat call. Switch to AUTO first.

How do I fix Rheem Furnace Blowing Cold Air - Causes & Fix?

Follow the step-by-step diagnosis below. The most likely fix is identified by checking power, sensor resistance, and control-board signals in order — using a multimeter and the part numbers documented in the parts reference table.

Can I keep running the equipment with this fault active?

Generally no. Faults on Hvac units are emitted when a sensor, safety, or control circuit is outside its operating envelope. Running through an active fault risks compressor, heater, or control-board damage. Diagnose and clear the fault first.

What part is most commonly replaced for Rheem Furnace Blowing Cold Air - Causes & Fix?

The most frequently replaced parts for Rheem Furnace Blowing Cold Air - Causes & Fix are listed in the Parts Reference section of this guide with OEM part numbers and typical price ranges. Check the table for direct replacements.

Is Rheem Furnace Blowing Cold Air - Causes & Fix a DIY repair or do I need a technician?

Sensor swaps, fan motor replacements, and condenser cleaning are typical DIY-level repairs. Anything involving refrigerant, gas, or high-voltage (>240V) work requires a licensed technician for both safety and code-compliance reasons.

Rheem Furnace Blowing Cold Air - Causes & Fix

Rheem Furnace Blowing Cold Air — What’s Happening

When a Rheem furnace blows cold air, the blower is running but the burners are not producing heat. This is a symptom, not a specific fault code. The furnace may be failing to ignite, losing flame after ignition, or shutting down the burners on a safety fault while the blower continues to move room-temperature air.

The exact cause depends on the flash code displayed on the integrated furnace control board. Common scenarios include ignition failure, flame sensor dropout, or a safety device like a high-limit or rollout switch opening and stopping the burners while the blower keeps running to clear heat or because the thermostat fan setting is incorrect.

Jump to Fix

Most Likely Causes

Thermostat fan set to ON instead of AUTO The blower runs continuously regardless of heat demand, circulating unheated air between cycles or when burners fail to light.
Dirty air filter or blocked airflow Restricted airflow causes the furnace to overheat and trip the high-limit safety, shutting off the burners while the blower continues to run.
Ignition failure from bad igniter or gas supply The igniter does not glow properly, gas is not reaching the burners, or the ignition sequence does not complete, so no flame establishes.
Dirty or failed flame sensor The flame sensor cannot prove flame presence, causing the board to shut the gas valve within seconds of ignition and leave only the blower running.
Open rollout or high-limit switch A safety switch has tripped due to overheating or blocked venting, preventing the burners from staying on or relighting.
Pressure switch or inducer problem The pressure switch does not close to prove draft, blocking ignition, often due to a weak inducer motor, blocked vent, or plugged pressure tubing.
Condensate drain clog on condensing models A blocked condensate trap or drain line can trigger a pressure or safety fault that interrupts burner operation while the blower runs.

How to Diagnose and Fix

Verify the thermostat is calling for heat and the fan switch is set to AUTO, not ON, to rule out continuous blower operation from the thermostat.
Inspect and replace the air filter if dirty, and check that supply registers and return grilles are open and unobstructed.
Read the LED flash code on the Rheem integrated furnace control board and cross-reference it with the unit’s service manual to identify any active fault or lockout condition.
Observe a complete ignition sequence from the inducer startup through flame establishment, watching for igniter glow, gas valve opening, flame lighting, and whether the burner stays lit or drops out.
If the burners do not ignite, check that gas is on at the meter and manual valve, inspect the hot surface igniter for cracks or failure to glow, and verify gas valve wiring and operation.
If the burner lights then shuts off within seconds, remove and clean the flame sensor rod with fine sandpaper or a soft cloth, check its position in the flame, and test for continuity and proper microamp signal.
Test rollout switches, high-limit switches, and the pressure switch for proper closure and reset, inspect the inducer motor and venting for blockage or restriction, and check pressure switch tubing for clogs or cracks.
On condensing models, inspect the condensate trap and drain line for clogs, flush or clear as needed, and verify the trap is properly filled and sealed to maintain draft.

Parts You Might Need

Part	Notes
Hot surface igniter	Amazon \| Replace if cracked, broken, or does not glow bright orange during ignition sequence.
Flame sensor	Amazon \| Clean first with fine abrasive; replace if cleaning does not restore flame proving.
Pressure switch	Amazon \| Replace if it does not close to prove draft when the inducer is running and tubing is clear.
Air filter	Amazon \| Standard consumable; replace at manufacturer intervals or when visibly dirty or restricted.

If your appliance also shows a code on the display, these match this problem:

When to Call a Pro

Call a qualified HVAC technician for any work involving gas supply, gas valve testing, ignition system replacement, or combustion venting. If you have cleared the filter and confirmed the thermostat fan setting but the furnace still does not produce heat or shows a fault code you cannot resolve, professional diagnosis with combustion analysis and electrical testing is the safe next step. Flame sensor issues and pressure switch diagnostics can often be handled by a homeowner comfortable with basic electrical testing, but igniter replacement and all gas-side troubleshooting should be left to a licensed pro. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.