Rheem furnace troubleshooting

Reviewed by Eric Grubbs

Rheem furnace not working? Wondering if you can fix it yourself or if you need to call an expert? You’ve come to the right place!

We’ve listed the most common issues below, along with corresponding Rheem furnace troubleshooting tips. Give our suggestions a try before calling a repairperson. You may save yourself the expense and hassle of a service visit.

Don’t want to deal with DIY? Hire an expert now.

Rheem furnace is not heating

Set your thermostat to “heat” and “auto.” If you set it to “on,” it will blow air constantly. If the furnace isn’t in a heating cycle, the air coming out of your vents may not feel warm.

Check the air filters throughout your home and in your furnace. You should change them every few months. If they get too dusty, they’ll prevent airflow throughout your HVAC system. You can purchase new filters on Amazon or at a nearby hardware store. Follow our furnace filter replacement guide for instructions on how to do this.

Check all the air vents in your home. The louvers should be open and free of obstructions like furniture, drapes, laundry piles, and other clutter. Blocked vents can also inhibit airflow.

If you can access your ductwork, examine it for holes and blockages. You can see some of your ducts by taking off the registers and looking inside with a flashlight. If debris has fallen in, remove it. If you see any leaks, repair them with UL181 Tape or sealant specified for ductwork repair. Consider hiring a duct cleaning company if you haven’t cleaned them recently.

If your furnace uses gas, check the gas valve inside. It’s a knob that likely has “on” and “off” labels. If the “on” and “off” labels are missing, you’ll know the valve is “off” if it is perpendicular to the gas piping. If it’s in line with the gas pipe, then it’s in the “on” position.

Check the pilot light if you have an older furnace (20+ years old). If it’s gone out, read your owner’s manual for instructions on how to re-light it.

Look at your burners and other components within the furnace. If they’re dirty, they may prevent ignition. With the furnace powered off, dust the inside with compressed air. You can also use a vacuum with a hand-held component with a soft bristle brush on the end. Burnt-on substances can be removed from your flame sensor and burners with an emory cloth.

If none of these Rheem furnace troubleshooting tips get your furnace heating again, call an expert.

rheem furnace troubleshooting fix

Rheem furnace is short cycling

Set your thermostat to “heat” and “auto.” Dust in and around the thermostat to ensure its sensors accurately read the temperature.

Check the air filters in the furnace and air returns. If excessively dusty, they may inhibit airflow and cause short cycling. Buy fresh filters on Amazon or at a nearby hardware store. Our furnace filter replacement guide has instructions to help you change yours.

Search your home for air leaks. Feel for drafts, especially near windows and doors. The Department of Energy has tips on how best to find air leaks. If you detect a leak, seal it with weatherstripping. Air leaks make it hard for the furnace to keep up, which may cause short cycling.

Check your air ducts for holes and blockages. Remove your registers and look in with a flashlight. Clean out any fallen debris inside and repair any holes with duct tape or sealant. If you can’t access all your ductwork, consider hiring a duct cleaning company for a thorough checkup.

Make sure your Rheem furnace flue is clear. It’s the metal tube that vents your furnace to the outside of your home. It may lead out through a wall or the roof. If there’s anything in the way, like snow or a bird’s nest, clear it away.

If these Rheem furnace troubleshooting suggestions don’t stop the short cycling, call an HVAC pro. They can get to the bottom of your issue.

Rheem furnace is running constantly

Set your thermostat to “heat” and “auto.” If you choose “on” instead of “auto,” your system will blow air constantly, even when it’s not in a heating cycle.

If that doesn’t solve your problem, dust in and around your thermostat with condensed air. Its sensors might be dusty and unable to register that it’s reached the set temperature.

Check the furnace filters and those in your air returns. If they are excessively dusty, they may block airflow and cause the furnace to strain. Purchase new filters on Amazon or at your local hardware store. Our furnace filter replacement guide has video instructions to help.

Search your home for air leaks. Feel for drafts near windows and doors. Seal them with weatherstripping or a draft stopper. If warm air is escaping, your furnace may have difficulty keeping up.

Also, check your air ducts for leaks or blockages. Remove your air registers and examine the inside with a flashlight. Clean out anything that’s fallen inside and fix any holes you can reach with UL181 Tape or sealant specified for ductwork repair. Consider hiring a duct cleaning company for a more thorough examination if you haven’t had your ducts cleaned in several years.

Finally, take a look at the limit switch in your furnace. It’s circular, with wires coming out on two sides. If this piece is damaged, it can cause your furnace to run constantly. If you’re an expert DIY-er, you may be able to replace it yourself following the instructions on our limit switch repair page. But in most cases, this is a job for a professional.

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Rheem furnace is making unusual noises

Rattling or clinking sounds may indicate an easy fix. Open your furnace cabinet and look inside for stray items that may have fallen in, especially screws or bolts that may have come loose. Check all fasteners and tighten them if needed.

Rheem furnace codes

Sometimes, your furnace may give you a clue about what’s wrong. Your Rheem furnace may have an LED display on the front, depending on its age. When it’s experiencing trouble, the furnace will display a code corresponding to the issue.

Below, we’ve listed some of the most common Rheem furnace codes and what they mean. For more information, refer to your Rheem furnace owner’s manual.

Rheem furnace codeWhat it meansTroubleshooting tips
0Standby modeN/A – normal operation
cdDehumidifier onN/A – normal operation
dFDefrost onN/A – normal operation
FContinuous fan onN/A – normal operation
H (flashing)Furnace calibratingN/A – normal operation
HActively heatingN/A – normal operation
d1No shared dataFurnace may not be communicating with thermostat.
10One-hour lockoutCall a professional. You may be able to get furnace running temporarily, but it requires attention.
11Failed ignitionCheck flame sensor, gas valve, and gas supply.
12Low flameCheck flame sensor, gas valve, and gas supply.
13Flame lostCheck flame sensor, gas valve, and gas supply.
14Unexpected flameCheck your furnace for fire. Call a pro.
22Main limit openFurnace is overheating. Check for system blockages and improper ventilation.
23Heat assist limit openFurnace is overheating. Check for system blockages and improper ventilation.
26Line and neutral reversedThis is an electrical issue. Call an electrician.
33Manual reset limit openCheck furnace temperature. If it’s OK, reset limit switch (usually a red button on a circular device).
44Low-pressure switch closed; inducer offCheck the inducer. This prevents dangerous backdrafts in your home.
45Low-pressure switch open; inducer on highAir intake is likely clogged.
46Low-pressure switch open; inducer on lowAir intake is likely clogged.
55High-pressure switch closed; inducer offCheck the inducer. This prevents dangerous backdrafts in your home.
57High-pressure switch openAirflow is blocked somewhere in the system.
60Blower fault; blower runningCheck blower for potential issues.
61Blower fault; blower not runningCheck blower for potential issues.
66Blower overspeed faultCheck blower for potential issues.
68No communication with blower motorCheck blower for potential issues.
77No communication with gas valveCheck gas valve for potential issues.
78Gas valve servo faultCheck gas valve for potential issues.
82Supply air temperature sensor faultCheck air temperature sensor for potential issues.
93Internal fault or control faultThis is an issue with the control board. Call a pro for help.

Rheem furnace troubleshooting resources

Rheem’s website has a page that offers some help for furnace issues. There’s also a Homeowner Resource Center where you can look up warranty details and information about parts.

If our Rheen furnace troubleshooting tips aren’t enough to get your furnace back up and running, call an HVAC pro. They can identify the issue and fix it for you.

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