Trane furnace 5 flashes — Flame sensed when it shouldn't be

What this error means

The board detects flame when no flame should be present — for example, a gas valve that isn't closing fully or a lingering flame after shutdown. Unlike the other flash codes, this is not a DIY item: out-of-sequence flame implies a possible gas-valve failure.

Symptoms

• 5-flash pattern on the status LED
• Burners glowing/running when the furnace should be off
• Gas smell (if ANY gas smell: leave, and call the gas utility from outside)

Try this first (safe DIY steps)

1. If you smell gas: don't operate switches — leave the area and call your gas utility's emergency line
2. Otherwise: shut the furnace off at the switch and its gas shutoff valve, and book service — do not power cycle repeatedly

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

When to call a technician

Immediately. Gas-valve diagnosis and replacement is licensed-technician work.