Armstrong furnace 11 flashes: Pressure switch stuck closed before the inducer started
Eleven flashes means the pressure switch was already closed before the combustion air inducer was activated. It must sit open at rest, and finding it closed means the interlock cannot be trusted.
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 pressure switch proves the inducer is genuinely moving air, and it does that by sensing suction. At rest, with the inducer off, it must be open. The control checks this before activating the inducer, because a switch stuck closed would prove a draft that does not exist — which would let the furnace fire into a flue that might be blocked. Allied Air's wording is precise about the timing: stuck closed prior to activation of the combustion air inducer, so this check happens before anything else in the sequence.
Most common causes
- Pressure switch contacts stuck or welded closed.
- The sensing hose pinched or kinked so that it traps pressure.
- Water in the sensing hose or the pressure tap holding the switch closed.
- A short in the pressure switch wiring, which is electrically indistinguishable from closed contacts.
- The wrong pressure switch fitted at a previous repair. These are rated per model and are not interchangeable.
How to diagnose it
- Note whether the inducer starts at all. On this fault the control stops before that step by design.
- Note whether the furnace was serviced recently. A hose or switch disturbed during other work is a common trigger.
- Check the condensate drain for backing up, since water reaching the sensing hose is a frequent cause.
- Distinguish this from the nine-flash code carefully. They are opposite halves of the same test and need different repairs.
How to fix it
- Clearing a blocked condensate drain is reasonable homeowner work and addresses one of the causes.
- The pressure switch, its hose and its wiring are technician work. The switch proves safe venting.
- Never jumper a pressure switch to get heat. It is the only thing between a blocked flue and a firing burner.
- Replace a failed switch with the exact part for the model, since the setpoint is model-specific.
Notes
Nine and eleven flashes are the two failure directions of one test — one says the switch will not close, the other says it will not open. Counting accurately matters more here than almost anywhere else in the set.
Related
- 9 flashes — Pressure switch failed to close, or opened during a heat demand
- 10 flashes — Watchguard — pressure switch opened five times during one heat demand
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 11 flashes means on every brand puts them side by side.
What the fix costs
This usually is the switch — which makes it the unusual pressure-switch code where the $150–400 part-and-labor range in the furnace repair cost guide describes the likely bill rather than the worst case. A switch found closed before the inducer has even started points at welded contacts, a stuck diaphragm, or sensing tubing pinched in a way that holds the switch closed — not at the flue problems that dominate the stuck-open codes. There is no blockage-clearing shortcut on this one; something physical is wrong at the switch or its tubing.
Do it yourself or call someone?
Call, and without much preamble. The check that failed happens before ignition, so the furnace has correctly refused to start — there is nothing to reset your way past, and no outdoor termination to inspect, because the fault is a switch proving a draft that cannot exist yet. Confirming which failure it is means opening the cabinet and working the sensing circuit, and the repair is the same visit. The one useful homeowner step is running the error recall so you can tell the technician whether eleven flashes is new or has a history.
The same fault on other control families
The at-rest stuck-closed check is near-universal: Carrier's code 23, Goodman's 2 flashes, Lennox's alert 224, and the ICP SmartValve's 2 flashes all report a pressure switch closed before the inducer runs. Allied's wording is the most precise about timing — stuck closed prior to activation of the inducer — but the defeated interlock is the same everywhere; see pressure switch codes.
What this looks like
From the outside, this usually shows up as the inducer spins up but the burners never fire — that walkthrough covers what to check in order, and when it stops being a homeowner job.