Rheem furnace 2 blinks: Pressure switch failure — switch remains open
Two blinks means the pressure switch stayed open when it should have closed. The furnace could not prove it was moving combustion air, so gas was never released.
Applies to: Rheem standard gas furnaces. Rheem states these codes do not apply to modulating, LXE, or two-stage models. Ruud and Weather King furnaces of the same generation share the platform.
What it means
The pressure switch proves the draft inducer is actually moving air before the control opens the gas valve. It closes when it senses the suction the inducer creates. This code means it never closed. Everything in the venting path can cause that — a blocked intake or exhaust, a full condensate trap, a weak inducer, a disconnected hose — and it is also the fault most often caused by something entirely outside the house. A vent termination blocked by snow, ice, leaves, or a nest produces exactly this, which makes a walk outside the most productive first check rather than anything in the basement.
Most common causes
- A blocked exhaust or intake pipe at the outside termination — snow, ice, leaves, insect or rodent nests.
- A condensate drain or trap that is full or blocked.
- The pressure switch 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 for the furnace.
- High wind at the termination on exposed installations.
How to diagnose it
- Look at the outside vent termination first. Highest yield, no tools required.
- Listen for the inducer. If it does not run at all the fault is upstream; if it runs and nothing follows, the switch is not seeing the draft.
- Check the condensate drain and trap for standing water.
- Note the weather. This appearing during the first hard freeze or a snowstorm points strongly at the termination.
- Distinguish carefully from four blinks, which is the opposite condition — a switch stuck closed rather than stuck open.
How to fix it
- Clear the vent termination if blocked, and keep both pipes clear of snow, ice, and vegetation.
- Clear a blocked condensate drain — reasonable homeowner work on most installations.
- The pressure switch, its hose, the inducer, and the vent system inside the cabinet are technician work.
- If vent sizing is wrong for the furnace, have it corrected rather than worked around.
- Never bypass the pressure switch. A blocked flue with a firing burner is how carbon monoxide enters a house.
Notes
If this appears on the coldest night and clears when milder, suspect ice at the vent termination. High-efficiency furnaces produce condensate at the exhaust and it can freeze around the pipe, progressively closing it.
Related
All codes for this manufacturer
Rheem, Ruud and Weather King furnace blink codes — every code, with what differs between models.
Not sure this is your brand?
The same count means something else on other furnaces. What 2 flashes means on every brand puts them side by side.