York furnace 3 red flashes: Pressure switch open, or first stage pressure switch open

Three red flashes means the pressure switch never closed, so the furnace could not prove it was moving combustion air and gas was never released.

Applies to: York, Luxaire and Coleman gas furnaces using the UTEC integrated furnace control boards documented in technical service letter ST-045-09. On single stage boards this is simply the pressure switch; on two stage boards it is the first stage switch. Stored in the error code array.

What it means

The pressure switch proves the inducer is moving enough air to carry combustion products safely out of the house before the gas valve opens. This code means it did not close. Everything in the venting path can cause it, and it is also the fault most often caused by something entirely outside the furnace — a vent termination blocked by snow, ice, leaves, or a nest. York's tables distinguish the single stage and two stage cases at the same flash count, with the two stage version specifically identifying the first stage switch, and a separate double-flash pattern for second stage.

Most common causes

• A blocked exhaust or intake pipe at the outside termination.
• A condensate drain or trap that is full or blocked.
• The sensing hose disconnected, cracked, kinked, or holding water.
• A weak or seized inducer motor, or a loose inducer wheel.
• A failed pressure switch that no longer closes at its rated pressure.
• Vent piping too long, with too many elbows, or the wrong diameter.
• High wind at the termination on exposed installations.

How to diagnose it

1. Look at the outside vent termination first — highest yield and no tools required.
2. Confirm whether the pattern is three single flashes or three double flashes, since those are different stages on two stage boards.
3. Listen for the inducer. If it runs and nothing follows, the switch is not seeing the draft.
4. Check the condensate drain and trap for standing water.
5. Note the weather, since freezing at the termination produces exactly this.

How to fix it

1. Clear the vent termination if blocked, and keep both pipes clear of snow, ice, and vegetation.
2. Clear a blocked condensate drain — reasonable homeowner work on most installations.
3. The pressure switch, hose, inducer, and vent system inside the cabinet are technician work.
4. Never bypass the pressure switch. A blocked flue with a firing burner is how carbon monoxide enters a house.

Notes

York using a double-flash pattern to separate second stage from first is easy to miss when counting quickly. Watching two or three full cycles before deciding is worth the extra half minute.

Related

• 3 double red flashes — Second stage pressure switch stuck open
• 6 red flashes — Pressure switch cycle lockout

Sources

• Johnson Controls Unitary Products technical service letter ST-045-09 — York UTEC furnace boards, fault code tables and retrieval procedure