Rheem furnace 1 blink: Limit circuit is open
On these condensing furnaces a steady single blink means the limit circuit is open. The furnace runs the inducer and the circulating blower to clear the heat and refuses to do anything else until the limit closes.
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 one blink means something else entirely — see the note below.
What it means
The control checks the limit circuit and, when it finds it open, energises the inducer and the conditioned air blower deliberately — that is the furnace moving air to bring the temperature down, not the furnace trying to run. Rheem's wording is that all other system functions are inoperable until the limit circuit closes, and that while the limit is open the red LED pulses at one blink per unit time. So this is not a stored fault code that survives the event; it is a live indication that reflects the state of the circuit right now, and it stops as soon as the limit closes. An open limit means the furnace exceeded its design temperature, and on a condensing furnace that almost always means airflow.
Most common causes
- A dirty or clogged air filter restricting airflow across the heat exchanger.
- Closed, blocked or covered supply registers and return grilles.
- A blower wheel loaded with dirt, or a blower motor running slow.
- Restricted, undersized or disconnected return duct.
- A failed limit switch that is open when it should be closed.
- A gas input set too high for the equipment.
How to diagnose it
- Check the air filter first. It is the most common cause and it is homeowner work.
- Confirm the supply registers and return grilles around the house are open and unobstructed.
- Note whether the blower is running while the burners are not — on this control that is the expected behaviour for this code, not a separate fault.
- Confirm the model number begins RC or RL before using this page. On a standard Rheem furnace one blink means a one-hour soft lockout instead.
How to fix it
- Replace a dirty filter and clear any blocked registers, then see whether the indication clears.
- If it returns with a clean filter and open registers, the restriction is in the ductwork or the blower, and that is technician work.
- A limit switch that is open with no overheat present is a failed switch, but that is a measurement rather than an assumption.
- Do not bypass the limit. It is the protection against the heat exchanger overheating.
Notes
The most important thing on this page is the model check. Rheem's standard flash code list assigns one blink to a one-hour soft lockout, which would send a reader looking for an ignition problem instead of an airflow problem.
Related
- Which blink code list applies — Rheem publishes two blink code lists that contradict each other
- 1 blink — Soft lockout, one hour
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 1 flash means on every brand puts them side by side.