Trane furnace 2 flashes: System lockout — retries or recycles exceeded
Two flashes means the furnace has used up its allowed ignition retries or recycles and stopped. It is a lockout, not a live failure — the attempts already happened.
Applies to: Trane and American Standard upflow, downflow and horizontal gas-fired direct vent condensing furnaces covered by Installer's Guide 18-CD29D1-14-EN, using the integrated furnace control described there.
What it means
Trane's integrated furnace control distinguishes retries from recycles, and this code covers both being exhausted. A retry is a fresh ignition attempt after a failure to light; a recycle is a restart after a flame was established and then lost. Either way, the control has a limit and this code means it has been reached. The furnace is not trying at the moment you read the code — it stopped some time ago. Understanding that changes what you look for: the question is not why it will not light now, but what happened during the attempts it already made, which usually comes down to gas, ignition, or flame detection.
Most common causes
- No gas reaching the burners — a closed valve, an empty propane tank, or a supply interruption.
- A failed hot surface igniter.
- A flame sensor coated with oxide, so a real flame goes undetected and the control treats each attempt as a failure.
- A flame sensor bent out of the flame path.
- Low or unstable gas pressure, so a flame lights and cannot be held.
- Poor grounding, which breaks the flame rectification circuit.
- A restricted flue producing a flame that will not stabilise.
How to diagnose it
- Check whether other gas appliances work. If none do, the problem is the gas supply.
- Check the furnace's manual gas valve is open, and on propane that the tank has fuel.
- Watch a start attempt if the furnace has a sight glass. Burners lighting and going out points at flame sensing or gas pressure; never lighting points at gas or the igniter.
- Note whether the furnace produces heat occasionally rather than never. Many controls release a lockout on a timer, and a furnace heating once every few hours is locking out repeatedly rather than working intermittently.
How to fix it
- Restore the gas supply if that is the cause.
- Replace the air filter and open closed registers — neither causes this directly, but both accompany related faults.
- Igniter replacement, flame sensor cleaning, and gas pressure testing are technician work, sitting in the ignition circuit and the gas train.
- Do not reset repeatedly to force a run. Each reset delivers gas to a burner that may not light it.
Notes
The retry and recycle distinction is worth mentioning to a technician if you have observed the furnace. A furnace that lights and loses flame is a different investigation from one that never lights, and this code covers both.