Now, look, if you’re staring at a cold house and a blinking LED on your Rheem furnace, I know exactly what you’re feeling. It’s frustrating when the machine just decides to quit on you. You might notice the blower motor running constantly while the igniter refuses to glow, or perhaps the unit is just sitting there like a brick. Don’t panic yet—while this code sounds like a death sentence for the electronics, I’ve walked plenty of folks through the diagnostic process to get the heat back on. It’s a hurdle, but it’s one we can clear.
⚠️ Warning: Check Manual First
For your safety and to avoid voiding the warranty, please check the official docs.
Quick Repair Specifications
| Metric | Details |
|---|---|
| Difficulty Level | Moderate (Involves electrical testing and wiring) |
| Estimated Time | 45 – 90 Minutes |
| Tools Needed | Digital Multimeter, 5/16″ Nut Driver, Needle-nose Pliers, Work Light |
| Estimated Cost | $150 – $450 (Depending on board model and warranty) |
Symptoms of Error 93
In my thirty years of turning wrenches, I’ve learned that the machine usually tells you what’s wrong before the code even pops up. If you’re dealing with an Internal Control Memory Fault, you’ll likely see the following:
- The Status Light Flash: You’ll see a specific sequence of nine amber or red flashes followed by three, or a digital readout showing “93” on the seven-segment display.
- The “Zombie” Blower: Many Rheem models are programmed to run the indoor blower motor constantly when a board fault is detected as a safety measure to prevent overheating. If the fan is blowing cold air and won’t stop, that’s a red flag.
- Ignition Failure: The furnace won’t even try to click the gas valve or spark the igniter. Because the memory is corrupted, the board doesn’t trust itself to manage the flame safely.
- Intermittent Lockouts: Sometimes the unit will work for a cycle and then go into a “hard lockout,” requiring you to flip the power switch just to get another thirty minutes of heat.
Technical Explanation of the Fault
When we talk about an “Internal Control Memory Fault,” we aren’t just saying the board is “broken.” We are talking about a failure in the EEPROM (Electrically Erasable Programmable Read-Only Memory) or the microprocessor itself. Here is why that happens:
- Voltage Spikes and Dirty Power: This is the number one killer. If you had a recent thunderstorm or if the local utility company had a “brownout,” the sudden surge can scramble the data stored on the board’s memory chip. It’s like a book with pages torn out; the furnace tries to read the instructions for the “Inducer Start” sequence, hits a blank page, and throws Error 93.
- Thermal Stress (Heat Cycles): Control boards are located inside the furnace cabinet. Over years of operation, the constant expansion and contraction from heating up and cooling down can cause “cold solder joints” or internal fractures in the silicon of the microchip. Eventually, a circuit trace breaks, and the memory becomes inaccessible.
- Grounding Issues: I’ve seen boards fry because the furnace wasn’t properly grounded. Without a solid path to ground, static electricity or stray voltage can back-feed into the DC side of the control board, nuking the sensitive memory components.
- Component Aging: Capacitors on these boards have a lifespan. When a capacitor fails to filter the power going to the microprocessor, the “noise” in the electricity can cause the processor to write “garbage data” into its own memory, leading to a permanent fault.
Troubleshooting & Replacement Instructions
Before you go spending a few hundred bucks on a new board, let’s make sure we’ve exhausted the simple fixes. Follow these steps carefully.
- The “Hard Reset” (Power Cycling):
I know it sounds too simple, but sometimes the memory just needs a clear slate. Locate the power switch (looks like a light switch) on the side of the furnace or flip the breaker. Leave it completely off for at least 10 minutes. This allows the capacitors on the board to fully discharge. Flip it back on. If the code clears and stays gone, you might have just had a temporary glitch. If it returns immediately, the board is toast.
- Inspect the Low Voltage Wiring:
Take your 5/16″ nut driver and remove the burner access door and the blower door. Locate the control board. Look for any wires that are charred, frayed, or loose. Sometimes a short in the thermostat wire (the thin ones) can mimic a board fault. Ensure the “R,” “C,” “W,” “G,” and “Y” wires are snug in their terminals.
- Check for “Ghost” Voltages:
Set your multimeter to AC Volts. Measure the incoming power at the “L1” and “Neutral” terminals on the board. You should see 115V to 125V. Now, check the voltage between Neutral and Ground. If you see more than 1 or 2 volts, you have a grounding issue that likely fried your board and will fry the new one if you don’t fix the house wiring first.
- Replacing the Integrated Furnace Control (IFC):
If the code 93 persists after a reset, you must replace the board. Pro tip: Take a high-resolution photo of every single wire on the old board before you unplug anything. Use needle-nose pliers to gently pull the wire connectors off. Unscrew the mounting screws, swap the board, and reconnect the wires exactly as they were in your photo. Ensure the board is mounted on its standoffs to prevent it from shorting against the metal chassis.
- Post-Installation Test:
Once the new board is in, restore power. The board should go through a “heartbeat” flash (usually a steady slow blink). Call for heat at the thermostat and watch the sequence: Inducer motor starts, igniter glows, gas valve clicks, and—boom—you’ve got blue flames.
SAFETY WARNING: High voltage (120V) is present inside the furnace cabinet. Always turn off the power at the breaker before touching any internal wiring.
How to Prevent Error 93
Once you’ve got the heat back on, you don’t want to be doing this again in two years. Here is how you protect that expensive new piece of silicon:
- Install a HVAC Surge Protector: I tell all my customers this: your furnace is a computer that happens to burn gas. You wouldn’t plug your $2,000 laptop directly into a wall without a surge strip, so why do it to your furnace? Install a dedicated HVAC surge protector (like an Intermatic or RectorSeal) at the furnace disconnect switch.
- Maintain Clean Filters: It sounds unrelated, but a clogged filter makes the blower motor work harder, drawing more Amps and creating more heat inside the cabinet. Excessive heat is the enemy of electronic components. Change your filters every 90 days, no exceptions.
- Keep the Area Dry: If your furnace is in a damp basement, use a dehumidifier. High humidity can cause micro-corrosion on the control board pins, leading to the kind of data corruption that triggers Error 93.
FAQ
Frequently Asked Questions
Q: Can I repair the memory chip on the board itself?
A: Technically? Maybe, if you’re an electrical engineer with a soldering station. Practically? No. These boards are UL-listed safety devices. If you mess with the internal circuitry and the furnace fails to shut off the gas later, you’re looking at a massive safety risk. If the board has a memory fault, the only professional recommendation is total replacement.
Q: Is Error 93 covered under warranty?
A: Most Rheem furnaces come with a 5 or 10-year parts warranty. If your unit was installed within that window and you registered it, the board itself should be covered. You’ll still have to pay for the labor unless you have a labor warranty with your installer. You’ll need the serial number of the furnace to check the status.
Q: Why did the error code change to something else after I reset it?
A: This is common. When the memory is failing, the board might throw a 93 (Memory Fault), then after a reset, it might throw a 68 (Blower Fault) because it’s still confused. If you see a “carousel” of different codes that don’t make sense, it almost always confirms that the central processor has failed.