What causes Rheem Gas Furnace 93?

24 VAC or a similar voltage reaching the main gas valve solenoid circuit when the control hasn't called for gas, usually from miswiring (Rheem's first listed cause). A welded relay on the control board that keeps voltage on the gas valve contacts after the inducer shuts off. The furnace control board failing its internal software test, meaning the control itself has failed.

How do I fix Rheem Gas Furnace 93?

Write down the code, then turn the thermostat off and switch off power to the furnace at its service switch or breaker. Wait a minute and turn power back on. Rheem says this lockout clears only by cycling power, not by turning the heat call off and on. If 93 comes right back, stop there. It points to a wiring problem on the gas valve circuit or a failed control board, and both involve the gas valve, so it's a job for an HVAC technician. If anyone recently added wiring at the furnace, such as a humidifier, thermostat or accessory, tell the technician; Rheem's first fix is to check for miswiring. Don't swap in a control board pulled from another furnace. Rheem warns this can load the wrong model data.

When should I call a pro for Rheem Gas Furnace 93?

Checking the furnace and gas valve wiring for miswiring that puts 24 VAC on the gas valve circuit unexpectedly. Replacing the furnace control (IFC) if the wiring is correct and 93 returns. Moving the original memory card (model data card) to the replacement control, since Rheem requires it to stay with the furnace. Matching the dip switch settings of the original control on the replacement board.

Code: 93🔥 Rheem Gas Furnace

Rheem Furnace Code 93: Internal Control Fault Detected

Q: What does Rheem Gas Furnace 93 mean?

Code 93 on a Rheem or Ruud gas furnace with a two-digit display means "Internal Control Fault Detected." It's a critical fault: the furnace won't run in any mode until it's cleared. Rheem gives two causes: 24 VAC (or a similar voltage) showing up on the main gas valve circuit when it shouldn't, usually from miswiring, or the furnace control board failing its own software self-test. Rheem says this fault should rarely if ever be seen in the field, and the usual fix is checking the wiring and then replacing the furnace control board. In Rheem's fault code table for the 802V furnace (installation instructions 92-24161-149-06, Table 14), code 93 is "Internal Control Fault Detected," a critical fault where the furnace will not operate in any mode. Rheem describes it as a severe fault that indicates either an internal microprocessor fault on the integrated furnace control (IFC) or voltage applied to the main gas valve solenoid when there should be none. If the furnace was heating, the gas valve closes immediately, the indoor blower stops, and the inducer runs its post-purge; after that, nothing else runs, thermostat calls included, until the fault is cleared. Because it can mean the microprocessor itself has failed, Rheem warns the heat call may not end normally and all outputs may simply shut off with the gas valve closed. Both the 802V and the R96V manuals list 93 under hard lockout: the control senses an unspecified internal fault, or voltage is detected on the gas valve contacts (a welded relay) that doesn't clear when the inducer cycles. Rheem says this lockout cannot be reset by cycling the heat call; lockouts clear once the original fault is fixed and power is turned off and back on. The manuals also note that if the control is in soft lockout with 93 active, the display alternates "93" and "10."

Reviewed 2026-10-24 · Based on 2 manufacturer & service sources

What the code means

In Rheem's fault code table for the 802V furnace (installation instructions 92-24161-149-06, Table 14), code 93 is "Internal Control Fault Detected," a critical fault where the furnace will not operate in any mode. Rheem describes it as a severe fault that indicates either an internal microprocessor fault on the integrated furnace control (IFC) or voltage applied to the main gas valve solenoid when there should be none. If the furnace was heating, the gas valve closes immediately, the indoor blower stops, and the inducer runs its post-purge; after that, nothing else runs, thermostat calls included, until the fault is cleared. Because it can mean the microprocessor itself has failed, Rheem warns the heat call may not end normally and all outputs may simply shut off with the gas valve closed. Both the 802V and the R96V manuals list 93 under hard lockout: the control senses an unspecified internal fault, or voltage is detected on the gas valve contacts (a welded relay) that doesn't clear when the inducer cycles. Rheem says this lockout cannot be reset by cycling the heat call; lockouts clear once the original fault is fixed and power is turned off and back on. The manuals also note that if the control is in soft lockout with 93 active, the display alternates "93" and "10."

Likely causes

24 VAC or a similar voltage reaching the main gas valve solenoid circuit when the control hasn't called for gas, usually from miswiring (Rheem's first listed cause)
A welded relay on the control board that keeps voltage on the gas valve contacts after the inducer shuts off
The furnace control board failing its internal software test, meaning the control itself has failed

Safe DIY checks

⚠ Before you start

Turn off power at the furnace/HVAC service switch and the breaker before opening panels. Shut the gas valve before any work near the burners, and never disconnect or alter the gas line. If you smell gas, leave the house and call your gas utility.

Write down the code, then turn the thermostat off and switch off power to the furnace at its service switch or breaker.
Wait a minute and turn power back on. Rheem says this lockout clears only by cycling power, not by turning the heat call off and on.
If 93 comes right back, stop there. It points to a wiring problem on the gas valve circuit or a failed control board, and both involve the gas valve, so it's a job for an HVAC technician.
If anyone recently added wiring at the furnace, such as a humidifier, thermostat or accessory, tell the technician; Rheem's first fix is to check for miswiring.
Don't swap in a control board pulled from another furnace. Rheem warns this can load the wrong model data.

🛠 When to call a pro

Checking the furnace and gas valve wiring for miswiring that puts 24 VAC on the gas valve circuit unexpectedly.
Replacing the furnace control (IFC) if the wiring is correct and 93 returns.
Moving the original memory card (model data card) to the replacement control, since Rheem requires it to stay with the furnace.
Matching the dip switch settings of the original control on the replacement board.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Furnace control board

Only the exact Rheem or Ruud replacement for your model, installed by a technician who moves the original memory card over.

Search eBay →

⚙

Multimeter

For a technician checking for stray 24 VAC on the gas valve circuit.

Search eBay →

⚙

Carbon monoxide alarm

Good insurance for any gas furnace, especially after gas valve or control work.

Search eBay →

Sources

Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.

Rheem Furnace Code 93: Internal Control Fault Detected

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Furnace control board

Multimeter

Carbon monoxide alarm

Related codes

Sources