Rheem furnace 1 blink: Soft lockout, one hour
One blink means the control has put itself into a one-hour soft lockout. It will release automatically, which is why the furnace appears to work briefly every hour and then stop.
Applies to: Rheem standard gas furnaces. Rheem states these codes do not apply to modulating, LXE, or two-stage models, which use different diagnostics. Ruud and Weather King furnaces of the same generation share the platform.
What it means
A soft lockout is a deliberate pause rather than a permanent shutdown. The control has met a condition it will not keep retrying immediately, so it stops for an hour and then tries the whole sequence again. That timing produces a distinctive and frequently misread symptom: the house gets a short burst of heat roughly every hour. People often describe this as the furnace working intermittently or struggling in cold weather. It is doing neither — it is failing, waiting out its lockout timer, and failing again in the same way. Recognising the hourly rhythm is the fastest way to tell a soft lockout from a furnace that is genuinely cycling.
Most common causes
- Repeated failure to establish or prove flame, which is the most common route into a soft lockout.
- No gas reaching the burners — a closed valve, an empty propane tank, or a supply interruption.
- A failed hot surface igniter.
- A flame sensor coated with oxide, so a real flame goes undetected.
- Low or unstable gas pressure.
- Poor grounding, which breaks the flame rectification circuit.
- A safety condition the control has chosen to retry on a timer rather than immediately.
How to diagnose it
- Note the hourly pattern. Heat roughly once an hour is the signature of this code and rules out several other explanations.
- Check whether other gas appliances work, which separates a supply problem from a furnace problem.
- Check the furnace's manual gas valve is open, and on propane that the tank has fuel.
- Watch a start attempt if the furnace has a sight glass. Whether the burners light at all is the key split.
- Note whether the blink count is genuinely one and not a longer pattern, since Rheem's standard code set is short and adjacent counts mean very different things.
How to fix it
- Restore the gas supply if that is the cause.
- Igniter replacement, flame sensor cleaning, and gas pressure testing are technician work.
- Do not reset the furnace repeatedly to clear the lockout. Each reset starts another sequence that may deliver gas to a burner that will not light it.
- Book service rather than living with hourly heat through a cold spell. The furnace is not coping — it is failing on a schedule.
Notes
Rheem explicitly scopes this code set to standard furnaces, excluding modulating, LXE, and two-stage models. Reading a two-stage Rheem furnace against this table will give the wrong answer, so the model matters before the count does.