Trane's integrated control keeps a diary: its last four faults, replayed on the red LED every time power returns, newest first, two seconds apart. A 2 in that replay is history — possibly last month's history. A 2 that shows as the standing code after the replay, while the furnace refuses to run, is tonight's lockout.
The lockout itself is generic by design: "retries or recycles exceeded" says the ignition sequence failed repeatedly, but not which link broke. The diary is the diagnosis — the faults stored before the 2 (often a 3 for draft, or the pattern of flame failures) tell the technician where to start. This is the strongest argument on the site for not power-cycling a Trane repeatedly: the board remembers what you need, until you make it forget.
2 flashes: System lockout — retries or recycles exceeded
Homeowner checks
The furnace tried to light or stay lit too many times and locked out. On power-up this board replays its last 4 faults, newest first, with a 2-second gap between codes — count carefully or you will merge two codes into one.
From the table: Red-LED flash codes — integrated furnace control — source: Trane UC Series Installer's Guide 18-CD19D5-10, diagnostic codes (read the document, fetched 2026-10-30). Covers: Trane/American Standard furnaces with the IFC covered by Installers Guide 18-CD19D5-10 (UC/AUH families and relatives). Green LED reads system state; the red LED flashes the faults.
Retries versus recycles
One word in the definition does real work. Retries = it never lit. Recycles = it lit, lost flame, lit again, lost it again. If your furnace audibly lights and runs briefly before quitting, you are in recycle territory — flame sensing and draft stability — even though the posted code is the same 2.
Homeowner checks — the safe list:
- Thermostat set to Heat, and set a few degrees above the room temperature.
- The gas shut-off valve at the furnace: handle in line with the pipe means open. If it is off, that is your answer — and ask yourself why it was off.
- Air filter: pull it and look. A matted filter causes more furnace faults than any broken part.
- One reset is fair: power off at the switch for 30 seconds, back on, and watch what it does. If it locks out again, stop resetting it — the code is telling you something real.
The two rules that outrank everything on this page.
1. Smell gas? Stop reading. Leave the house and call your gas utility or 911 from outside. No code is worth diagnosing through a gas smell.
2. Never bypass a safety switch — no jumping a pressure switch, no taping a limit, no propping a rollout. Those switches are the only thing between a furnace fault and a fire or carbon-monoxide problem. This library explains codes; it does not teach repairs inside the cabinet.
One honesty note before the tables: codes change between control boards, sometimes inside the same brand and the same decade. Every table below names the board and the manual it was transcribed from. The chart glued inside your own blower door is the final word for your furnace — if it disagrees with this page, believe the door.