Armstrong Air Furnace 11 flashes: What It Means & How to Fix It
Compiled & reviewed by the HVAC Flash Codes editorial team · Updated 2026-06-25 · confidence: high
⚠️ Try the safe checks, then a pro
What does Armstrong Air furnace 11 flashes mean?
Pressure switch stuck closed prior to activation of the combustion-air inducer — the switch read closed before the inducer started, when it should be open. Most often caused by A pressure switch stuck/welded closed or failed.
What your furnace LED does. The diagnostic light blinks 11 flashes, pause, repeat — that pattern is Armstrong Air furnace 11 flashes.
What Armstrong Air furnace 11 flashes means
Pressure switch stuck closed prior to activation of the combustion-air inducer — the switch read closed before the inducer started, when it should be open.
Common causes
A pressure switch stuck/welded closed or failed
A pressure-switch hose connected wrong or pinched
Residual draft/condensate holding the switch closed
Homeowner-safe steps to try
There's no safe homeowner adjustment for this fault — leave the furnace controls alone
You may note the code and do a single power cycle
Schedule professional service if it persists
When to call a licensed HVAC technician
If the basic checks below don't clear the code, the fault recurs, or anything involves the gas valve, burners, flame sensor or wiring, stop and book a licensed HVAC technician. Repairs to the combustion or gas system are not DIY.
⚠️ Safety first. Gas furnaces burn fuel and produce combustion gases. If you ever smell gas (a rotten-egg or sulfur odor), hear hissing, or your carbon-monoxide alarm sounds, do not touch light switches, thermostats, or the furnace — leave the home immediately and call your gas utility's emergency line or 911 from outside. Homeowners should limit themselves to simple, safe steps: setting the thermostat, checking and replacing the air filter, confirming the furnace switch and breaker are on, keeping supply registers and return grilles open, and clearing snow, ice, or debris from outdoor vent and intake terminations. Never bypass, jumper, or reset safety switches (limit, flame-rollout, or pressure switches), never open the gas valve or burner compartment, and never attempt combustion, electrical, or control-board repairs yourself. Error codes point toward a problem but are not a substitute for proper diagnosis — when in doubt, turn the system off and call a licensed HVAC technician. Keep working carbon-monoxide detectors on every level of your home.
When to call a pro: Call a licensed HVAC technician to test/replace the pressure switch and check the hoses — a stuck-closed switch defeats a key safety check. Don't bypass it. If you smell gas, leave and call your gas utility or 911 from outside.
Armstrong Air furnace 11 flashes FAQ
What does Armstrong Air furnace 11 flashes mean?
Pressure switch stuck closed prior to activation of the combustion-air inducer — the switch read closed before the inducer started, when it should be open.
What causes Armstrong Air furnace 11 flashes?
Common causes: A pressure switch stuck/welded closed or failed; A pressure-switch hose connected wrong or pinched; Residual draft/condensate holding the switch closed.
Can I fix Armstrong Air furnace 11 flashes myself?
You can safely try: There's no safe homeowner adjustment for this fault — leave the furnace controls alone; You may note the code and do a single power cycle; Schedule professional service if it persists. Call a licensed HVAC technician to test/replace the pressure switch and check the hoses — a stuck-closed switch defeats a key safety check. Don't bypass it. If you smell gas, leave and call your gas utility or 911 from outside.
Sources: firstsupply.com. General information for homeowners, not professional advice — confirm against your furnace's manual and a licensed technician.