Armstrong furnace 1 flash: Reverse line voltage polarity
One flash means the incoming line voltage has line and neutral reversed. It is a wiring error rather than a component failure, and it almost always follows electrical work.
Applies to: Allied Air Enterprises A80UH1E and 80G1UHE gas furnaces with the -02 integrated control, sold as Armstrong Air, AirEase, Concord and Ducane.
What it means
Flame detection works by rectification — passing a very small current through the flame to ground — which only functions if the supply is connected the right way round. So the control checks polarity before it will operate, and refuses to run when the check fails. Allied Air separates this from grounding, which gets its own code, so one flash points specifically at line and neutral being swapped rather than at a missing ground. 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 recently replaced outlet or newly run circuit wired incorrectly.
- A loose neutral connection in the circuit.
- 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 the two-flash grounding code has also appeared. Both together usually means one supply problem rather than two.
- 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 fault that developed.
- Have the ground path checked at the same time, since the adjacent code covers it and the two often travel together.
- Do not attempt to bypass the check. The control is refusing to run because it cannot trust its own flame detection.
Notes
Allied Air giving polarity and grounding separate codes is more informative than the manufacturers that group them. If you see one and not the other, that genuinely narrows the fault.
Related
All codes for this manufacturer
Armstrong Air, AirEase, Concord and Ducane furnace codes — every code, with what differs between models.
Not sure this is your brand?
The same count means something else on other furnaces. What 1 flash means on every brand puts them side by side.
What the fix costs
This code rarely ends in a parts bill. Reversed polarity is a wiring fault — line and neutral swapped at a receptacle, the service switch, or a junction — so what you are paying for is the finding, not a component. Expect a standard diagnostic or service call, $75–150 in most US metros per the furnace repair cost guide, often credited against any repair, with the correction itself usually minor wiring work on top. The expensive version of this fault is ignoring it and paying for flame-sensing parts that were never broken.
Do it yourself or call someone?
Thinking is DIY; measuring is not. It is worth noting what changed before the code appeared — a replaced service switch, electrical work in the house, a generator hookup, a new receptacle — because one flash on a furnace that ran clean for years almost always follows a wiring change, and that history shortens the visit. Confirming polarity means putting a meter on live line voltage inside the cabinet, and correcting it at an outlet or panel is licensed electrical work in most places. Do not swap wires on a hunch; get an electrician or HVAC technician.
The same fault on other control families
Swapped line and neutral gets a dedicated code on several controls: Carrier signals it with a rapid flash, Goodman shows EA, Lennox raises E111, and Trane's S9V2 display shows E6.1. The mechanism — flame rectification needing the supply connected the right way round — is identical on all of them. The full family is on grounding & polarity codes.
What this looks like
From the outside, reversed polarity itself usually shows up as the burner lights and then drops out a few seconds later, since the control can’t get a dependable flame reading with line and neutral swapped — that walkthrough covers what to check in order.