Armstrong furnace 2 flashes: Improper earth ground
Two flashes means the furnace is not properly earthed. Flame detection depends on a solid ground path, so the control refuses to run without one.
Applies to: The -02 integrated control on Allied Air Enterprises’ A80UH1E and 80G1UHE gas furnaces carries this code across every badge it ships under: Armstrong Air, AirEase, Concord, and Ducane.
What it means
Flame rectification passes a tiny current from the flame sensor, through the flame, to ground. Without a proper earth the circuit is incomplete and the control cannot reliably tell whether a flame is present — which is the one thing it must be certain about before keeping the gas valve open. Allied Air gives this its own code rather than grouping it with polarity, which is genuinely useful: a two-flash code points at the ground path specifically, and the first things to check are the connections rather than the supply orientation.
Most common causes
- A missing or disconnected ground wire at the furnace chassis.
- A loose blower motor ground connection.
- A loose low voltage common ground.
- Corrosion at a ground connection.
- A grounding problem in the house wiring feeding the furnace.
- Work done at the furnace that disturbed a ground and did not restore it.
How to diagnose it
- Establish whether the furnace has been serviced recently. A control board or blower motor replacement disturbs grounds that this code depends on.
- Note whether the one-flash polarity code has also appeared. Both together usually indicate one supply problem.
- Note whether other intermittent faults have appeared alongside it — poor grounding produces weak flame signal codes and ignition faults too.
- Do not test grounding yourself unless qualified.
How to fix it
- This is technician work at the furnace chassis and its supply.
- Ask for every ground connection to be checked and tightened, particularly the blower motor ground and the low voltage common ground.
- If the fault followed recent service, call whoever did the work.
- If the grounding problem traces back to house wiring rather than the furnace, that needs an electrician.
Notes
Grounding is one of the most under-appreciated causes of furnace faults. It produces weak flame signals, ignition failures and apparently random lockouts across every manufacturer, and it is invisible unless the control checks for it explicitly — as this one does.
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 2 flashes means on every brand puts them side by side.
What the fix costs
Budget for the diagnosis, not a part. A missing earth ground is usually a connection problem — a loose ground screw, a corroded lug, a fault upstream in the branch circuit — and the fix is restoring the path rather than replacing anything on the furnace. The furnace repair cost guide puts a diagnostic or service call at $75–150, often credited if work follows. The costly failure mode here is misdiagnosis: a bad ground starves the flame-sensing circuit, so it gets treated as a flame sensor fault, and the real cause survives visit after visit while the cleaning bills accumulate.
Do it yourself or call someone?
With power off at the service switch, looking is fine: a ground wire hanging loose at the cabinet or a visibly corroded connection is sometimes obvious without touching anything. Everything past looking is a call. Verifying ground quality means measurements on a live circuit, and correcting grounding at the panel or a junction box is licensed electrical work. Do not keep running the furnace on resets while the ground is suspect — flame proving depends on this circuit, and the control is telling you it cannot trust it.
The same fault on other control families
Sixteen codes across ten control families describe this same failure of the flame-rectification ground reference — the full list is on grounding & polarity codes. Lennox splits it by severity, with E112 shutting the system down for no ground while alert 117 only warns of a poor one; Trane reports it as E6.2, and the Goodman/York board lineage flashes 9 red on both tables. Allied's two-flash code sits closest to the Lennox warning: a dedicated, specific pointer at the ground path.
What this looks like
From the outside, a missing earth ground usually shows up the same way: the burner lights and then drops out a few seconds later, because the flame-rectification circuit can’t complete without one — that walkthrough covers what to check in order.