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.
- Lockout after five failed ignition attempts — Rheem, Ruud and Weather King *RC 92+ full size upflow and *RL 90+ full size downflow condensing furnaces, per installation instructions 708503a
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.
Do it yourself or call someone
This is one of the least DIY-able codes on Rheem's standard list. The two-blink fault sends you outside with a broom; this one does not, because a switch stuck closed is a failed or defeated safety device rather than a blocked pipe. The homeowner share is three things: count the blinks carefully — twice, since two and four are opposite conditions — check whether the condensate drain is backing up, which is the one cause with a homeowner-accessible fix, and note any recent service, since a disturbed hose or a wrong replacement switch is a common trigger. Everything else is meter-and-manometer work on the interlock that proves the flue is clear, and it belongs to a technician. Do not power-cycle the furnace hoping the switch frees itself, and never jumper it: a switch that always reads closed would let the burner fire into a flue that might be completely blocked.
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.
The same fault on other brands — and on Rheem's other list
A pressure switch found closed before the inducer starts is a defeated-interlock fault most control families define separately from the stuck-open version: Carrier's 58MCB logs it as code 23 (switch did not open), Goodman boards show two flashes, Lennox communicating systems raise alert 224, and Trane's S9V2 furnaces display E31 — the full set is on the pressure switch codes hub. The twist unique to Rheem: on its own *RC 92+ and *RL 90+ condensing furnaces the identical fault carries three blinks, not four, which is exactly the kind of cross-list trap the model check at the top of this page exists to catch.
What the fix costs
A pressure switch replacement typically runs $150–400 per the furnace repair cost guide. The guide's standing advice for pressure switch codes — check for a blocked flue before condemning the switch — cuts the other way here: a switch stuck closed is usually genuinely the switch, its hose, or its wiring rather than the venting, so this is one of the pressure switch faults where the part is more often the real answer. A shorted wire or water in the sensing hose can present identically and costs only the diagnostic fee to find, typically $75–150 and often credited against the repair. Insist on the exact switch for the model: the setpoint is model-specific, and a near match defeats the point of the interlock.
What this looks like
From the outside, this usually shows up as the furnace starts and stops in short bursts — that walkthrough covers what to check in order, and when it stops being a homeowner job.