Armstrong furnace 10 flashes: Watchguard — pressure switch opened five times during one heat demand
Ten flashes means the pressure switch opened five times within a single heat demand and the control locked out. That count is documented, and it points at a marginal draft rather than an absent one.
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
Allied Air specifies the threshold exactly: five openings during one heat demand. That precision changes the diagnosis. A switch that never closes is a blockage; a switch that closes and drops out five times in one cycle is a draft that is marginal — present, but not reliably enough to hold. Conditions that produce that pattern come and go rather than being constantly present: wind at the termination, a condensate trap filling during the run, ice forming progressively, or an inducer weakening as it heats. Those are harder to find than a blocked pipe, because the furnace often works when a technician arrives.
Most common causes
- A partly restricted vent or intake, where draft is marginal rather than absent.
- A condensate drain that backs up during a cycle and clears between them.
- Wind at the vent termination disturbing the draft intermittently.
- An inducer weakening and unable to hold its output steadily.
- A pressure switch operating at the edge of its setpoint.
- A sensing hose partly obstructed, so pressure fluctuates.
- Ice forming progressively at the exhaust termination during a long run.
How to diagnose it
- Note that this is a repeated fault within one cycle, which points at an intermittent condition rather than a blockage.
- Check the outside vent termination for partial restriction, and note the weather — wind and freezing conditions both fit.
- Check the condensate drain for slow drainage rather than complete blockage.
- Note how long the furnace runs before faulting, since a consistent interval suggests something accumulating.
- Recall the stored history. Nine-flash codes preceding this one confirm the pattern.
How to fix it
- Clear the vent termination and condensate drain if either is partly restricted. Both are within homeowner reach.
- The pressure switch, its hose and the inducer are technician work.
- Have the vent system assessed properly if the restriction is not obvious. Marginal draft is harder to find than absent draft and produces exactly this code.
- Record when it happens — time of day, weather, how long the furnace had run. That information is something only the householder can supply and it materially helps.
Notes
A manufacturer publishing the exact trip count is genuinely useful. It tells you the furnace tolerated four interruptions before stopping, which means the draft is present most of the time — and that rules out the simple explanations.
Related
- 9 flashes — Pressure switch failed to close or opened during heat demand
- Error code recall — Ten stored faults that survive a power cut
All codes for this manufacturer
Armstrong Air, AirEase, Concord and Ducane furnace codes — every code, with what differs between models.