Rheem / Ruud gas furnaces (80% and 90%+ with integrated furnace control): quick sheet

Covers: Rheem and Ruud 80% and 90%+ residential gas furnaces. Older integrated controls flash a single LED (often labelled OK or STATUS); many newer controls show two-digit numeric codes on a small display. Code meanings vary by control generation; this sheet lists only codes that two independent sources agree on.

Single sourceBrands: Rheem, Ruud7 components

Rheem and Ruud share the same platforms. Know which control you have before reading codes: a flashing LED board and a numeric-display board use different code tables. On 90%+ models the condensate trap and vent/intake pipes are the first suspects for pressure-switch faults.

Safety first

Gas valve, burners, heat exchanger and venting are blocked: refer to a licensed HVAC/gas technician.
Read the code before cutting power.
Never bypass the rollout or pressure switch.

How it works

Standard induced-draft sequence: inducer on, pressure switch closes, pre-purge, hot surface igniter warm-up, gas valve opens, flame sensor proves flame, blower starts after the heat-on delay.

If flame is not proven after the allowed ignition attempts, the control enters a lockout that lasts about one hour before it tries again on its own. Cycling power or the thermostat also resets it, but the cause must be fixed.

Numeric-display controls show the operating state (for example standby, heat, cool or fan) and fault numbers. 90%+ models add a condensate trap and PVC vent/intake; a full trap or wet pressure tubing makes the pressure switch open.

Some models can be twinned (two furnaces sharing one duct system and thermostat); twinning faults only apply to those installations.

Components & tests

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Official manufacturer documentation

Always confirm values against the tech sheet for the exact model.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): Large stainless refrigerator set flush between kitchen cabinets by Alex Qian, Pexels License

Diagnostic guides for this appliance

Guide · Furnace

Reading furnace LED flash codes by brand family (Carrier, Goodman, ICP, Rheem)

The flash code narrows the fault to one circuit before you open anything. Read it with power on, identify the board family, then use the door label to confirm. Only codes that two independent sources agree on are listed here.

8 steps ~10 mineasy

Guide · Furnace

Flame sensor microamp test and cleaning (measuring flame signal)

Measure the actual flame current in series with a µA DC meter before and after cleaning. A clean sensor with a low reading points to ground, wiring, board or burner flame problems rather than the rod itself.

8 steps ~30 minmoderate

Guide · Furnace

Furnace inducer (draft) motor not starting

Work from mechanical to electrical: does the wheel turn freely, is 120 V reaching the motor, and is the board sending it. A seized motor is replaced as an assembly; no output from the board points to the board relay or a safety input.

8 steps ~40 minmoderate

Other furnaces manuals

Manual · Furnace

Carrier / Bryant 80% gas furnaces (58ST, 58SB, 58SC, 312/315 families): quick sheet

Carrier, Bryant and Payne non-condensing (80% AFUE) single-stage and two-stage upflow/multipoise furnaces with an amber status LED and two-digit status codes. Covers families such as Carrier 58ST/58SB/58SC and Bryant 312/315. Newer communicating and variable-speed boards add codes not listed here.

9 components5 common failuresCarrier, Bryant, Payne

Manual · Furnace

Goodman / Amana 80% single-stage gas furnaces (GMS8, GMH8, GM9S80, GC9S80): quick sheet

Goodman and Amana non-condensing (80%) single-stage furnaces with a single red or green diagnostic LED: GMS8 / GMH8 (older), GM9S80 / GC9S80 (current) and Amana/Daikin badged equivalents. For the 96% GM9S96 / GMVC96 see the separate condensing quick sheet.

8 components5 common failuresGoodman, Amana, Daikin

Manual · Furnace

ICP 80% gas furnaces (Heil, Tempstar, Comfortmaker, KeepRite, Arcoaire): quick sheet

International Comfort Products (ICP, a Carrier company) non-condensing single-stage furnaces such as the N8MSN / N8MPN style models, sold under several brand names with the same control board. Single LED flashing in groups.

7 components5 common failuresHeil, Tempstar, Comfortmaker, KeepRite, Arcoaire, Day & Night