Rheem Furnace Not Heating — What’s Happening
A Rheem furnace that is not heating is a symptom, not a single fault code. It can map to several conditions including ignition failure, flame loss, flame sense faults, pressure switch faults, limit or rollout switch trips, or blower and control issues. The exact cause depends on the specific fault code or LED flash pattern displayed on your control board.
Common codes tied to no heat include Code 10 (ignition lockout after multiple failed attempts), Code 11 (failed ignition), Code 12 (low flame sense signal), Code 13 (flame lost during the heating cycle), Code 22 (limit switch open from overheating), Code 33 (rollout switch open), Code 45 or 57 (pressure switch faults from vent or intake restriction), Code 61 (blower fault), and Code 93 (control board failure). Each of these codes points to a different root cause, so identifying the flash pattern is the first step in diagnosis.
Most Likely Causes
- Dirty flame sensor The flame sensor rod gets coated with soot or oxidation over time, weakening the flame signal and causing Code 12, Code 13, or ignition lockout.
- Closed or blocked gas supply A closed manual gas valve, empty propane tank, or low gas pressure will prevent the burners from lighting or cause flame loss mid-cycle.
- Restricted airflow from dirty filter or blocked return A clogged air filter or obstructed return grille restricts airflow through the heat exchanger, causing the limit switch to open and shut down heating.
- Blocked vent, intake, or pressure switch tubing Ice, debris, or disconnected tubing on the pressure switch or vent piping prevents the inducer from proving draft and stops the ignition sequence.
- Failed ignitor A cracked or weak hot-surface ignitor will not reach the temperature needed to ignite the gas, causing Code 11 or repeated ignition failure.
- Faulty pressure switch or inducer motor A stuck pressure switch diaphragm or worn inducer motor bearing can prevent the switch from closing and block the call for ignition.
- Failed control board or blower motor Control board relay failures, blower motor faults, or capacitor issues can prevent the furnace from completing the heating cycle or communicating correctly with the thermostat.
How to Diagnose and Fix
- Read the fault code or count the LED flashes on the control board and record the pattern before doing anything else.
- Verify the thermostat is calling for heat and check that the R and W wiring terminals at the furnace are secure and making good contact.
- Check the manual gas valve at the furnace inlet and confirm it is fully open and that the gas supply to the home is on.
- Inspect and replace the air filter if it is dirty, and confirm all return grilles and registers are open and unobstructed.
- Inspect the vent and intake piping on the roof or exterior wall for blockage, ice, or animal nests, and clear any obstructions.
- Remove the burner door and visually inspect the flame sensor rod for soot or white oxidation, then clean it gently with fine steel wool or emery cloth.
- Check the inducer motor for free rotation and listen for draft when the thermostat calls for heat, then inspect the pressure switch tubing for cracks, kinks, or disconnection.
- Measure line voltage at the furnace: you should see 115 VAC between L1 and neutral and 115 VAC between L1 and cabinet ground, as specified in Rheem’s service documentation.
Parts You Might Need
| Part | Notes |
|---|---|
| Rheem flame sensor | Amazon | Match the sensor length and bracket style to your furnace model. Clean before replacing. |
| Rheem hot surface ignitor | Amazon | Handle only by the ceramic base. Verify amperage and wiring connector type before ordering. |
| Rheem pressure switch | Amazon | Match the pressure rating stamped on the switch body. Confirm draft and tubing integrity before replacing. |
| Rheem furnace air filter | Amazon | Check the filter size on the existing filter frame or blower door label. |
Related Error Codes
If your appliance also shows a code on the display, these match this problem:
- Rheem Furnace 2 Flashes error code
- Rheem Furnace 3 Flashes error code
- Rheem Furnace 4 Flashes error code
When to Call a Pro
Call a qualified HVAC technician if you are not comfortable working around gas appliances, if the fault code returns after you have corrected the obvious causes, or if the diagnosis points to ignition components, the gas valve, the control board, or the inducer motor. A technician can verify gas manifold pressure, measure flame sense microamps, check for proper grounding and phasing on the power supply, and safely replace ignition or control components. Do not bypass safety switches or attempt repeated manual resets without identifying and correcting the underlying fault, as this can damage the control board or create an unsafe condition. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.