Rheem furnace 3 blinks: Pressure switch closed when it should be open
Before starting the inducer the control checks the pressure switch, and it should be open. If it is found closed and stays closed for ten seconds, the furnace reports three blinks and will not proceed.
Applies to: Rheem, Ruud and Weather King *RC 92+ full size upflow and *RL 90+ full size downflow condensing furnaces, per installation instructions 708503a. On Rheem's standard gas furnaces three blinks means an open limit switch instead.
What it means
This check happens before the inducer runs, which is what makes it meaningful. With no inducer running there is no suction, so a correctly working pressure switch must be open. Finding it closed tells the control that the switch cannot prove anything — a switch that is always closed will read closed whether the flue is clear or completely blocked, so the interlock is useless and the furnace refuses to light. Rheem's instructions state that if the pressure switch is closed the heat mode sequence will not continue, and if it remains closed for ten seconds the red LED blinks three times repetitively until the fault clears. The wording is worth noting: it clears when the condition clears, so this is a live indication rather than a stored lockout.
Most common causes
- A failed pressure switch with welded or stuck contacts.
- A short in the pressure switch wiring, which looks identical to a closed switch.
- A pressure switch of the wrong specification fitted during a previous repair.
- A switch jumpered or bypassed during earlier service and never restored.
- In rare cases, strong wind or a vent condition holding the diaphragm over with the inducer off.
How to diagnose it
- Confirm the model number begins RC or RL before acting on this. On a standard Rheem furnace three blinks is an open limit switch, which is a completely different repair.
- Note whether the furnace has been serviced recently, since a jumpered switch left in place is a real and dangerous cause.
- Note whether the inducer ever starts. On this code it should not, because the check happens first.
- There is nothing here a homeowner can safely check inside the cabinet.
How to fix it
- Technician work. It involves the safety interlock that proves the flue is clear.
- Expect the switch and its wiring to be checked for a short before the switch is condemned.
- If a jumper is found across the switch, it must be removed, and the reason it was fitted needs to be found.
- A replacement switch must match the specification for that model, not merely fit the fitting.
Notes
This is the count where the two Rheem lists diverge most dangerously. Read as an open limit switch, a reader would go looking at filters and airflow while the actual fault is a defeated safety interlock.
Related
- 3 blinks — Limit switch open
- Which blink code list applies — Rheem publishes two blink code lists that contradict each other
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 3 flashes means on every brand puts them side by side.