Trane furnace 3 flashes — Pressure switch error

What this error means

The draft pressure switch is open when it should be closed (or closed when it should be open). Causes: blocked vent or intake (check the exterior termination — snow and ice are seasonal classics), a failing draft inducer, or on condensing furnaces a blocked condensate drain.

Symptoms

• No ignition; inducer may run continuously
• 3-flash pattern on the status LED

Try this first (safe DIY steps)

1. Check and clear the exterior vent/intake termination
2. On high-efficiency models, check the condensate drain isn't clogged or frozen
3. Power off 30–60 seconds and restore

Safety: power off before any physical intervention. Never bypass covers or interlocks — fuser areas run hot enough to burn.

When to call a technician

If it returns with clear venting: pressure switch ($150–$400) or inducer motor ($400–$1,100 installed) diagnosis.