Trane S9V2, S9X1, S9X2 and S9B1 condensing furnace showing E09: meaning and exact next steps

Model-specific

What is true of this model and not of its siblings

Two switches again

Trane's E09 covers an inducer limit and a condensate pressure switch, so the cause can be heat or water.

Condensate

A condensing furnace makes water that must drain freely.

The vent

A blocked vent can heat the inducer and open the limit.

Cold weather

Frozen discharge lines stop condensate.

A technician's job

Switch testing and drain cleaning.

Prevention

Check the drain line each autumn.

A trap that has filled

The condensate trap holds a small amount of water to prevent exhaust from escaping through the drain. If the drain line behind it is blocked, the trap overfills and the switch opens, which stops the furnace. Clearing the line or the trap fixes it.

A line that freezes

If the condensate drains outdoors, the water can freeze in the line in cold weather and block it. A technician may insulate the line or reroute it, and may add a heat cable where the code allows.

Inducer limit

The inducer has its own thermal limit, which opens if the inducer overheats. A blocked vent or a failing motor can cause this. If the drain is clear and the code remains, ask the technician to test the inducer.

Telling the two causes apart

If you see water on the floor, a full trap or a drain that runs slowly, the condensate switch is the likely cause. If the drain is dry and the inducer housing is hot to the touch after the furnace has stopped, the inducer limit is more likely. Do not touch hot parts; describe what you see.

Keeping the drain clear

Pour nothing down the trap without the manual's say-so. A technician flushes the line with water, checks the slope and looks for a loose or cracked fitting. If the drain goes to a pump, check that the pump's float moves and the pump runs.