Rheem furnace 4 blinks: Pressure switch failure — switch remains closed
Four blinks means the pressure switch was found closed when it should have been open. It is the opposite of the two-blink fault and needs a different repair.
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 must sit open when the inducer is off, and the control verifies that before starting a cycle. A switch stuck closed would prove a draft that does not exist, which would allow the furnace to fire into a flue that might be blocked — so finding it closed at rest, the control refuses to proceed. The distinction from two blinks matters a great deal in practice. Two blinks sends you outside to look at the vent termination; four blinks sends a technician to the switch, its hose, and its wiring. Miscounting between them wastes a visit.
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 during a previous repair — these are rated per model and are not interchangeable.
- Debris in the pressure tap.
How to diagnose it
- Count carefully and confirm the pattern repeats after a pause. Two blinks and four blinks are opposite conditions.
- Note whether the inducer starts at all. On this fault it usually does not, because the control stops before that step.
- Note whether the furnace was serviced recently, since 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.
How to fix it
- Clearing a blocked condensate drain is reasonable homeowner work and addresses one of the causes.
- The pressure switch, its hoses, 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. The setpoint is model-specific and a near match is not a match.
Notes
Because Rheem's standard code set is short, adjacent counts carry very different meanings. Counting twice before acting is worth the extra minute here more than on manufacturers with longer code lists.
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 4 flashes means on every brand puts them side by side.