Trane furnace 6 flashes: 115 volt AC power reversed, or poor grounding
Six flashes means the line voltage supply has line and neutral reversed, or the furnace is not properly grounded. It is a wiring fault rather than a component failure.
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
Flame detection works by rectification, which passes a very small current through the flame to ground. That only works if the supply is connected the right way round and the furnace has a solid ground path, so the control checks both before it will operate. This code means the check failed. It is worth recognising as a wiring fault rather than a broken part, because it almost always follows electrical work or a new installation. A furnace that ran for years and suddenly shows this usually means something in its supply circuit has been changed or has come loose.
Most common causes
- Line and neutral reversed at the furnace, at a junction box, or at the outlet feeding it.
- A missing or disconnected ground wire at the furnace.
- A loose neutral connection in the circuit.
- A recently replaced outlet or newly run circuit wired incorrectly.
- A furnace that has been moved, replaced, or reconnected.
- A control board that has failed in a way that misreads the supply.
How to diagnose it
- Establish whether any electrical work has been done recently — in the house generally, not only at the furnace.
- If the furnace is newly installed or reconnected, treat this as an installation fault rather than a developed failure.
- Note whether other faults have appeared alongside it. Reversed polarity and poor grounding also produce weak flame signal and igniter codes, so a cluster usually has one cause.
- Do not test the supply yourself unless you are qualified to work at a live panel.
How to fix it
- This is electrical work on the furnace supply and belongs to a licensed electrician or heating technician.
- If the furnace was just installed or reconnected, call whoever did the work — this is a wiring error, not a developed fault.
- Have the ground path checked as well as the polarity, since this code covers both.
- Do not attempt to bypass the check. The control is refusing to run because it cannot trust its own flame detection.
Notes
Because the same conditions break flame sensing, a furnace showing this alongside a history of ignition faults usually has one electrical cause behind all of them. Fixing the supply often resolves several apparently unrelated codes at once.
Related
- 9 flashes — Ignitor circuit problem, or low voltage between neutral and 24 volt common
- 8 flashes — Low flame sense signal
All codes for this manufacturer
Trane and American Standard furnace flash codes — every code, with what differs between models.
Not sure this is your brand?
The same count means something else on other furnaces. What 6 flashes means on every brand puts them side by side.
What the fix costs
This fault usually ends in a corrected wire rather than a new part, so the bill is mostly the visit: a diagnostic call runs $75–150 per the repair cost guide, often credited against work done. If the polarity or ground fault traces to the house wiring rather than the furnace circuit, an electrician's visit replaces or joins the HVAC one. The expensive version of this code is the unrecognised one — reversed polarity breaks flame sensing, and furnaces carrying this fault have a way of accumulating paid-for igniters and flame sensors that were never the problem.
DIY or call a pro
None of this one is homeowner work, which is unusual for a code with such a cheap fix. Confirming polarity and ground quality means meter work at live line-voltage connections, and correcting them means opening the panel, junction box, or disconnect. What a homeowner can usefully supply is the history: whether the furnace was recently installed, moved, or reconnected, and whether any electrical work has happened in the house — that context often locates the fault before a meter does. If the furnace is newly installed, this is a callback to the installer, not a repair.
The same fault on other brands
Swapped line and neutral gets its own code on many controls, and the site's grounding and polarity hub collects all of them. Equivalents of this code's polarity half include one flash on the Allied -02 control used by Armstrong and AirEase, and Goodman EA. Trane folding poor grounding into the same code is the less common choice — its own seven-segment controls split the two into E6.1 and E6.2.
What this looks like
From the outside, this usually shows up as the burner lights and then drops out a few seconds later — that walkthrough covers what to check in order, and when it stops being a homeowner job.