10 components coveredField manual · Furnace
Trane / American Standard S8X1 and S8X2 80% gas furnaces: quick sheet
Covers: Trane and American Standard S-Series non-condensing 80% AFUE multipoise gas furnaces: S8X1 (now sold by Trane as the '80 Single-Stage') and S8X2 (now the '80 Two-Stage'). American Standard sells the same S8X1/S8X2 model numbers (tier naming differs between sources: Silver vs Gold). Model pattern: S8X1 or S8X2 + cabinet width letter (A 14.5 in, B 17.5 in, C 21 in, D 24.5 in) + input in MBH (040, 060, 080, 100, 120) + M (multipoise) + blower size digit (3, 4 or 5 nominal tons of airflow) + PS + revision letters, e.g. S8X1B060M4PSC, S8X1B080M4PSCA, S8X2B060M4PSC, S8X2D120M5PSC. Search terms: S8X1, S8X2, S8X1B, S8X2B, Trane 80 single stage, Trane 80 two stage. Does not cover variable-speed S8V2 or older XR80/XV80 boards (their codes can differ).
The S8X1 and S8X2 are Trane's mainstream 80% AFUE induced-draft furnaces, 34 in tall and about 28 in deep, installable upflow, downflow or horizontal. Both use a tubular aluminized-steel heat exchanger, inshot burners, a 120 V silicon nitride hot surface igniter and a 9-speed (9-tap) constant-torque ECM blower. The S8X1 has a single-stage gas valve; the S8X2 adds a two-stage valve and a second pressure-switch stage. Faults are reported by an LED on the integrated furnace control (IFC), read through the window in the blower door.
Safety first
- Gas valve, manifold pressure, burners, heat exchanger and venting work are blocked: refer to a licensed gas technician.
- A rollout trip can mean flue products are spilling; check CO, do not reset repeatedly, and refer.
- Never jumper a limit, rollout or pressure switch to keep the furnace running.
- Lock out 120 V before touching wiring; the board is polarity-sensitive.
How it works
On a W call the IFC checks that the pressure switch is open, starts the PSC inducer, waits for the pressure switch to close, purges, then heats the silicon nitride igniter and opens the gas valve for the trial for ignition. The flame sensor must prove flame by rectification or the board closes the valve and retries; after the retry limit it locks out.
Once flame is proven the board runs the heat-on delay and starts the constant-torque ECM blower on the heat tap selected on the board. When the call ends the valve closes, the inducer post-purges and the blower runs through the heat-off delay.
S8X2 (two-stage): low fire is roughly 65% of rated input (example: S8X2B060 is listed at 39,000 BTU/h low and 60,000 BTU/h high input). High fire is called by W2 or by the board's internal timer when a single-stage thermostat is used, and it needs the second pressure-switch stage to close.
The limit string (main limit and rollout switches) is in series with the gas valve circuit. An open limit drops the valve and keeps the blower running. Line voltage is polarity-sensitive: reversed hot/neutral or a poor ground can show as a polarity fault or as failure to prove flame.
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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): Condensing gas furnace with PVC vent pipes and metal ductwork in a utility room by Wtshymanski, CC BY-SA 4.0
