Rheem and Ruud furnace code 93: internal control fault

Furnace control display or LED

93

“INTERNAL CONTROL FAULT”

(-)92P & (-)(-)92MSP, (-)92T & (-)(-)92MSX, (-)95P & (-)(-)95MSP, (-)95T & (-)(-)95MSX, (-)801S / (-)801P UPFLOW/HORIZONTAL & (-)(-)801MSS / (-)(-)801MSP; (-)(-)80MSS / 80MSP, (-)801S / (-)801P DOWNFLOW & (-)(-)80DSS / 80DSP, (-)801T UPFLOW/HORIZONTAL & (-)(-)80MSX, (-)801T DOWNFLOW & (-)(-)80DSX · 92-24161-118-16 p. 87; 92-24161-154-03 p. 87; 92-24161-111-17 p. 87; 92-24161-120-16 p. 87; 92-24161-142-15 p. 39; 92-24161-143-14 p. 34; 92-24161-144-09 p. 39; 92-24161-145-10 p. 34
Technician

What it means

93 is the furnace control reporting a fault in itself. The fault card calls it a severe fault that should rarely, if ever, be found in the field, and gives two meanings: an internal microprocessor fault on the furnace control, or voltage on the main gas valve solenoid when there should be none. The furnace does not run in any mode while it is active 95P: 92-24161-111-17, p. 94; 96V: 92-24161-124-12, p. 120.

If 93 comes up during heating, the gas valve closes at once and the flame goes out, the blower stops, and the furnace shuts down with an inducer post-purge. After that nothing runs, thermostat calls included, until the fault clears. The card warns that with an internal microprocessor failure the call for heat may not end as expected; all outputs are then switched off and the gas valve closed as soon as the fault is sensed 92-24161-111-17, p. 94.

93 can come with a hard lockout or a one-hour soft lockout. The installation instructions list two hard-lockout cases with 93: the control senses an unspecified internal fault, or it detects voltage on the gas valve contacts (a welded relay) that does not clear when the inducer cycles. In both, cycling the call for heat does not reset it 801T: 92-24161-144-09, p. 40; 96V: 92-24161-124-12, p. 121. When the voltage on the gas valve circuit goes away once the inducer stops, the control uses a one-hour soft lockout instead 92-24161-144-09, p. 40, and in a soft lockout with 93 active the display alternates 93 and 10 92-24161-111-17, p. 88. The same instructions say any lockout can be cleared immediately provided that the fault that caused it has been cleared and the power to the unit is turned off and on again 92-24161-144-09, p. 40. That describes the board, not an owner step.

In the 96P code list 93 has fault priority 1, so it is shown ahead of every other code in that list 92-24161-122-12, p. 88. On the 96V and 97V diagnostics charts only 30, open fuse, ranks above it (96V-chart; 97V-chart).

The card’s causes are 24 VAC or a similar voltage reaching the main gas valve solenoid circuit unexpectedly, and a furnace control software test failure, which the card equates with a failed furnace control. Its solutions are to check for mis-wiring in the furnace and to replace the furnace control 92-24161-111-17, p. 94.

Check these first

Rheem’s owner’s manuals have no code list and no reset (92-20802-128-03; 92-20802-130-02). For a furnace that will not operate, the last of their operating instructions gives two steps 92-20802-128-03, p. 4; 92-20802-130-02, p. 4:

1. Turn off the gas to the furnace by “To Turn Off Gas To The Appliance”: shut off the manual gas valve in the gas supply piping outside the furnace casing, set the thermostat to its lowest setting, turn off all electric power to the appliance if service is to be performed, remove the burner access door, turn the gas control knob or switch to OFF and replace the door 92-20802-128-03, p. 4. In that list the power step is conditional, but the manual’s warning is to turn off electrical power to the furnace before removing the front access door 92-20802-128-03, p. 7, and its operating instructions turn off all electric power before the burner access door is removed 92-20802-128-03, p. 4. Full steps: shutting the furnace down.
2. Call your service technician or gas supplier 92-20802-128-03, p. 4.

One of the two causes involves the gas valve circuit. If the gas valve fails to shut off the gas supply, the owner’s manual says to turn off the manual gas valve to the furnace before turning off the electrical supply 92-20802-128-03, p. 1.

The card’s solutions, checking for mis-wiring in the furnace and replacing the furnace control, are service work 92-24161-111-17, p. 94.

When to call a licensed technician

• Checking the furnace for mis-wiring, including voltage reaching the main gas valve solenoid circuit when it should not 92-24161-111-17, p. 94.
• Replacing the furnace control 92-24161-111-17, p. 94.
• On the communicating furnaces, the memory card goes with the furnace: when the control is replaced, the card must be removed from the old control, kept with the furnace and plugged into the new control 92-24161-124-12, p. 121. The manual says the card should never be removed from the furnace except during replacement of the control, and warns against using a control or memory card from another furnace or component 92-24161-124-12, p. 92.

The owner’s manuals say installation and service must be performed by a qualified installer, service agency or the gas supplier 92-20802-128-03, p. 1.

Notes for different models

Series	Where	Wording	Source
92P, 92T, 95P, 95T, 801S, 801P, 801T	code list	“INTERNAL CONTROL FAULT”	92-24161-111-17, p. 87; 92-24161-144-09, p. 39
92P, 92T, 95P, 95T, 2017 revisions	fault card	“INTERNAL CONTROL FAULT DETECTED”	92-24161-111-17, p. 94
96P, 96T, 2017 revisions	code list, priority 1	“INTERNAL FAULT”	92-24161-122-12, p. 88; 92-24161-157-04, p. 88
96P, 96T, 2017 revisions	fault card	“INTERNAL CONTROL FAULT DETECTED”	92-24161-122-12, p. 98
96P, 96T, first editions	code list	no 93	92-24161-122-01, p. 88; 92-24161-157-00, p. 88
802P	code list	no 93; the troubleshooting legend has “Internal control fault”, priority 1	92-24161-146-05, pp. 40, 51
96V, 97V, 98V, 802V, 801T Ultra Low NOx	fault card	“INTERNAL CONTROL FAULT DETECTED”	92-24161-124-12, p. 120; 92-24161-126-04, p. 104; 92-24161-148-07, p. 73; 92-24161-164-01, p. 40
Fault code label 92-103343-01-00 (listed on the RGGE and RGJF support pages)	label, no models printed	“Internal Fault”	92-103343-01-00, p. 1

The 801 series manuals have 93 in the code list and the hard-lockout rules, but no fault cards 92-24161-144-09, pp. 39–40. The 801T Ultra Low NOx and 98V card titles were read from the page images; their text could not be extracted, so this page does not paraphrase them 92-24161-164-01, p. 40; 92-24161-159-03, p. 101. On the 96V diagnostics chart 93 is a critical fault (fault level 2) at priority 1 (96V-chart).

For Ruud, the documents show only the replacement-parts line “www.myrheem.com/myruud.com” in the 802P manuals 92-24161-146-05, p. 50; 92-24161-147-04, p. 46 and the model name R801T on both a Ruud and a Rheem specification sheet (G22-556 Rev 8; G11-662 Rev 7); none ties a Ruud furnace to a series on this page.

Related Rheem and Ruud codes

• 10 “1 HOUR LOCKOUT”
• 14 “Unexpected Flame”

See also

• Heat pump vs gas calculator
• HVAC and furnace tax credits in 2025 and 2026: 25C, 25D, 30C

Other gas furnaces: Carrier, Goodman, Lennox

All Rheem and Ruud codes

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