How do you fix Armstrong flashes?

This needs an electrician rather than a heating technician. The furnace is reporting a fault it did not cause. Have the supply to the furnace checked for loose connections and adequate conductor size. Full steps and safety notes are on this page.

Armstrong furnace 13 flashes: Low line voltage

Thirteen flashes means the incoming line voltage is too low. This is a supply problem outside the furnace, and replacing furnace parts will not fix it.

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

The control monitors its own supply voltage and reports when it falls below the acceptable range. That is worth having as a distinct code, because low voltage produces symptoms that look like component failures: motors draw more current and run hot, relays chatter or fail to pull in, and controls behave erratically. Without this code, a furnace on a sagging supply would present as a series of unrelated faults. With it, the diagnosis points outside the furnace entirely — to the circuit feeding it, the panel, or the utility supply.

Most common causes

A utility supply problem, particularly during peak demand or a brownout.
An undersized circuit feeding the furnace.
A loose or corroded connection in the supply, causing voltage to sag under load.
A shared circuit with a large intermittent load on it.
A long cable run with excessive voltage drop.
Running from a generator with poor voltage regulation.

How to diagnose it

Note whether other appliances show symptoms — lights dimming when a large load starts is a useful clue.
Note whether the fault correlates with time of day, which would suggest a utility or peak-demand problem.
Note whether the furnace has been running on a generator, which is a common and easily forgotten cause.
Note whether the fault appeared after electrical work in the house.
Recall the stored history — repeated low voltage codes interleaved with other faults suggest the voltage is the root cause of all of them.

How to fix it

This needs an electrician rather than a heating technician. The furnace is reporting a fault it did not cause.
Have the supply to the furnace checked for loose connections and adequate conductor size.
If the problem is at the utility side, report it to the supply company.
Do not have furnace components replaced before the supply has been checked. A new motor on the same sagging supply will fail the same way.

Notes

This is the furnace code most likely to be reporting a problem elsewhere in the building. It is worth acting on even if the furnace is otherwise working, because sustained low voltage shortens the life of every motor in the system.

All codes for this manufacturer

Armstrong Air, AirEase, Concord and Ducane furnace codes — every code, with what differs between models.

What the fix costs

This code's bill often is not an HVAC bill at all. Low line voltage originates in the circuit feeding the furnace, the panel, or the utility supply, so the fix belongs to an electrician or the power company; the furnace-side spend is typically a $75–150 diagnostic (furnace repair cost guide) confirming the furnace is healthy and the supply is not. The hidden cost is in ignoring it: undervoltage makes motors draw more current and run hot, and the blower is the expensive thing that suffers — $400–1,500 to replace per the blower motor cost guide. Treated promptly, thirteen flashes is cheap. More supply-side codes: power supply codes.

Do it yourself or call someone?

Safe observations, all from outside any panel: do the lights dim when the furnace or another large appliance starts; does the code appear only when specific loads run; has the utility been working in the neighborhood. Those answers route the call correctly between electrician, utility, and HVAC. Not safe: anything inside the electrical panel, and the assumption that a code pointing outside the furnace means the furnace can keep running indefinitely on a sagging supply — relays that chatter under low voltage are cycling the gas train more than it was designed for.

What this looks like

From the outside, this usually shows up as the furnace is completely dead — that walkthrough covers what to check in order, and when it stops being a homeowner job.

This can also show up as the furnace not turning on at all — that page is a 5-minute checklist before calling anyone.

Sources

Allied Air Enterprises — A80UH1E and 80G1UHE Installation Instructions 507330-03, Table 7: Diagnostic Codes for -02 Control

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.