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.
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 1 flash means on every brand puts them side by side.