The short answer
On an Armstrong Air furnace in Northern Virginia, a pressure switch code means the furnace couldn’t prove its exhaust has a clear way out, so it won’t open the gas. The usual causes are a clogged condensate drain, a blocked vent pipe, cracked or water-filled switch tubing, or a weak inducer motor. Which code you see depends on the model year: 2, 3 or 6 flashes on older furnaces, 9, 10 or 11 flashes on the 2022 and newer 13-flash models, and E223 to E227 on furnaces with a number display.
If you smell gas, skip all of it. Leave the house and call the gas company and 911 from outside. If a carbon monoxide alarm is going off, get everyone out first (what to do when the CO alarm sounds).
Pressure switch codes by model
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| Model and year | Display | Pressure switch codes |
|---|---|---|
| A801D, A951A, A931A, A951S | Red light, up to 9 flashes | 2: closed with the inducer off. 3: open with the inducer on. 6: pressure switch cycle lockout. |
| A952V two-stage | Red light, up to 9 flashes, plus a green light | 2: closed with the inducer off. 3: low-fire switch, rollout or aux limit open. 6: cycle lockout. Green flashing: high pressure switch not closed. |
| A96UH1E (2022), A951E (2023), A801E | Red light, up to 13 flashes | 9: failed to close, or opened during a heat call. 10: opened 5 times in one call. 11: stuck closed before the inducer starts. |
| Two-stage, variable and 2026 K models | Number display | E223, E224: low switch failed open or closed. E225, E226: high switch. E227: low switch opened while lighting or running. E271, E272: retries or recycles used up on the switch. E228: inducer calibration (A97MV and A96MV only). |
AirEase uses the same A model numbers, and Ducane and Concord use the matching G numbers, so the same codes apply. The full tables for every code are in Armstrong Air furnace codes.
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What the switch is doing
Before the gas valve opens, the inducer fan pulls air through the burners and out the vent. The pressure switch is a small round switch with a rubber hose to the inducer or the vent. It closes only when the pull is strong enough, which proves the exhaust can get out. No proof, no gas. That’s why it trips: it’s doing its job.
Stuck closed is a different problem. The switch reads closed before the inducer even starts, which usually means the switch itself or its wiring failed. Allied’s service manual flags a low switch that stays closed more than 150 seconds into a heat call.
On a two-stage furnace, a slow low-fire switch doesn’t always stop the heat. Allied’s service manual says the inducer goes to high speed and the furnace lights on high fire, then drops to low after 10 to 20 seconds. A furnace that roars at every start can be telling you the low switch is slow.
What you can check, and what a tech checks
For E223, E224 and E227, Allied’s manual tells the installer the same thing every time: check the pressure where the switch closes, measure the operating pressure, and inspect the vent and inducer for a restriction. That’s a job with a manometer. What you can check yourself:
- The vent pipes outside. Two white plastic pipes on a high-efficiency furnace. Snow, leaves, a nest or frost at the end blocks them.
- Water near the furnace, or gurgling. A clogged condensate trap backs water into the tubing and the switch can’t close. Condensate drain clogs shows the signs.
- Reset once. Thermostat from Heat to OFF and back to Heat. The furnace also retries on its own after 60 minutes. Take a photo of the code before you reset anything. A reset can clear what’s showing, and that number saves the tech time and you money.
- Never bypass the switch. Jumpering it lets the furnace burn gas with nowhere for the exhaust to go. That’s how carbon monoxide gets into a house.
What it usually turns out to be
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| The cause | How a tech confirms it | Our price |
|---|---|---|
| Clogged condensate trap or drain | Water backed up in the trap or tubing | $175 to $420 |
| Water or a crack in the switch tubing | Tubing checked and blown clear | Priced in writing |
| Blocked or sagging vent pipe | Pressure at the switch, vent checked end to end | Priced in writing |
| Weak or failing inducer motor | The pressure it makes against what the switch needs | Priced in writing |
| Failed pressure switch | Stays open with good pressure, or closed with none | Priced in writing |
| Control board | Switch and wiring good, the code stays | $550 to $1,180 |
The switch, inducer and vent work gets priced in writing after the diagnostic, because the parts differ across the A and G models. The diagnostic is a flat $99.
Our heating check is $67 per system, through December 31: furnace, heat pump or boiler. On a furnace, for $229 (regularly $467) we also pull the blower wheel and clean it blade by blade. A yearly check is where a slow drain gets spotted before it trips the switch on the first cold night.
If the repair is a big one on an older furnace, get a second look before you spend it. Our free second opinion costs you nothing, and the estimator shows what a new system costs with $1,500 off already in the price.
Codes and warning lights from every brand, in one place: furnace and AC error codes.
Call or book a furnace repair
Call (703) 997-9757. We answer day or night. Or book online and pick a time. The diagnostic is a flat $99, and you see the repair price in writing before we touch anything. Furnace running fine and you want to keep it that way? Book the $67 heating check from goswiftpro.com/cookiesoffer (book by November 30) and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276. We work on Armstrong Air, AirEase, Ducane and Concord furnaces all over Northern Virginia: furnace repair.
Questions people ask
What causes an Armstrong Air pressure switch to trip?
Usually a clogged condensate drain, a blocked vent pipe, cracked or water-filled tubing on the switch, or a weak inducer motor. The switch trips because it can’t prove the exhaust has a clear way out.
What does 9 flashes mean on an Armstrong Air furnace?
On 13-flash models like the 2022 A96UH1E and 2023 A951E, 9 flashes means the pressure switch failed to close or opened during a heat call. On older 9-flash models, 9 flashes is incorrect line voltage phasing.
What does E227 mean on an Armstrong Air furnace?
The low pressure switch opened while the furnace was lighting or running. Allied’s manual says to check the switch pressures and inspect the vent and inducer for a restriction.
Can I bypass the pressure switch on my furnace?
No. It’s the switch that keeps the furnace from burning gas when the exhaust can’t get out. Bypassing it risks carbon monoxide in the house.
