Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
Trane 5 Flashes Error Code — What It Means
Five flashes on a Trane furnace LED means the pressure switch is stuck open. The pressure switch is a safety device that confirms the induced draft blower is moving enough air to safely exhaust combustion gases. When the switch stays open, the control board sees no airflow confirmation and won’t allow ignition. This code appears immediately at startup, before the igniter even energizes. The switch itself is often fine — the more common culprits are blocked vents, a failing draft motor, or a condensate backup in the pressure switch tubing.
Common Causes
- Blocked or kinked pressure switch hose — The small rubber hose from the draft motor housing to the pressure switch can collapse, crack, or get clogged with condensate. A blocked hose makes the switch read zero pressure regardless of motor speed.
- Clogged condensate drain — On high-efficiency (90%+) Trane furnaces, condensate backs up into the collector box and can flood the pressure switch port, preventing it from closing.
- Weak or failed induced draft motor — If the draft motor runs but at reduced speed (bad bearings or capacitor), it may not generate enough differential pressure to close the switch.
- Failed pressure switch — The switch diaphragm can tear or the switch contacts can fail open permanently. Test by temporarily jumping the switch terminals with the motor running (only to diagnose — never run with a bypassed switch permanently).
Step-by-Step Fix
- Inspect the vent pipes — Check the PVC exhaust and intake pipes outside the house for blockages: bird nests, ice dams, debris. Clear any obstruction. This is the easiest fix and takes 2 minutes.
- Check the pressure switch hose — Disconnect the small rubber hose from both ends and blow through it. Any obstruction or restriction means replace the hose ($2 part). Look for cracks where it connects to the collector box.
- Clear the condensate drain — On 90%+ units, pour a cup of water into the condensate trap and confirm it drains freely. Clear the trap with a wet-dry vac if it’s backed up.
- Test the draft motor — Listen for it to spin at startup. It should run for ~30 seconds before ignition is attempted. If it hums but doesn’t spin, the start capacitor is likely bad.
- Reset the system — Power cycle after repairs. If the switch closes (you’ll hear a click when the draft motor reaches speed), the fault clears and ignition proceeds.
Parts Often Needed
| Part | Notes |
|---|---|
| Pressure switch | Match the water column rating on the old switch (e.g., -0.65” WC) |
| Draft motor run capacitor | Cheap fix if motor hums but won’t start |
| Pressure switch hose (3/8” ID) | Cut to length; sells by the foot |
| Condensate trap | Replace if cracked or permanently clogged |
Technician Tips
Trane furnaces typically flash error codes through the LED on the integrated furnace control (IFC) board. Code 11 (no previous code) is the startup default — if you see this with a no-heat call, check for power at the IFC. Code 12 means blower on after power-up — normal after a reset. Code 13 means limit switch fault — this is often a dirty filter or restricted return. Code 14 means ignition failure — check gas pressure before condemning the igniter. Trane uses silicon nitride igniters that last longer than standard carbides but are more fragile during handling.
Estimated repair time: Most Trane ignition faults take 30-45 minutes to diagnose and fix. Limit switch and blower motor issues run 1-2 hours.
Need Replacement Parts?
Before ordering, match the HVAC part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
If the draft motor is confirmed running at speed and the vent pipes are clear, but the switch still won’t close, a tech should verify static pressure with a manometer before condemning the switch. An incorrectly rated replacement switch will fail in the same way.