Rheem furnace one-blink lockout: four trials or four flame failures
Rheem's one-blink code means no flame sensed after four ignition trials, or four flame failures in one heat call. Which one happened changes the diagnosis.
What this means
Rheem publishes the one-blink code as no flame sensed after four ignition trials, or four flame failures during one call for heat. Those are two different histories: in the first the burner never established a flame, and in the second it lit four times and the signal was lost each time. To clear it, Rheem has the owner interrupt the 115 volt supply, or switch the thermostat off, for a count of five to ten seconds.
Equipment and model context
Rheem residential gas furnaces covered by the published technical FAQ
- Rheem residential gas furnaces with electronic ignition and flame rectification
This code and reset method come from Rheem's published gas furnace technical FAQ and apply to the Rheem furnaces it covers. Ruud furnaces share much of the Rheem platform but their own literature governs, and a single flash on another manufacturer's control means something else entirely.
What you may notice
- The furnace attempts to light several times and then stops, with the diagnostic LED giving a single repeating blink.
- The burner is audible for a few seconds on each attempt and then goes quiet.
- The furnace works after a reset and locks out again on a later cycle.
Likely causes
- Supply polarity or phasing that is wrong breaks the rectification path Rheem relies on to confirm a flame.
- Deposits on the sense rod insulate it, which Rheem gives as a reason rectification does not occur.
- Manifold gas pressure set outside specification changes the flame itself, and Rheem attaches that to failed sensing.
- Rheem assigns pressure-switch faults to separate two-blink and four-blink patterns, so they should not be folded into a one-blink diagnosis.
| What happened on each attempt | Which half of the code applies | Where the fault sits |
|---|---|---|
| No burner sound at any point | Four failed ignition trials | Gas supply, igniter, gas valve, control, or wiring |
| Burner audible then silent within seconds | Four flame failures in one call | Flame sensing, polarity, grounding, or gas pressure |
| Burner ran a minute or more before stopping | Neither, this is not the lockout pattern | Airflow and the limit circuit |
| Two or four blinks instead | A different Rheem code | Pressure-switch circuit; use that code's service path |
| Lockout recurs within days of a reset | The underlying cause was not removed | Service, rather than another reset |
Diagnostic paths
You can hear the burner light on each attempt
Standing near the furnace, each attempt produces a brief burner sound before the unit goes quiet again, repeating a few times before it stops trying.
That is four flame failures rather than four failed ignitions. Note it, because Rheem's causes for that half of the code are flame sensing, polarity or phasing, and manifold gas pressure rather than the igniter.
Nothing lights at any point
The inducer runs, there may be a glow or a click, and no burner sound follows on any of the attempts.
Check whether other gas appliances in the house work, then record whether the igniter glows or sparks and whether a gas-valve click occurs. No burner flame across four trials is the ignition-failure half of the code; it does not by itself identify which component stopped the sequence.
The LED is actually showing two or four blinks
The repeating pattern contains two blinks or four blinks rather than one blink.
Stop using this one-blink page. Rheem lists an open pressure switch under the two-blink pattern and a closed pressure switch under the four-blink pattern. Record the exact pattern and use the matching model literature or service path.
It locked out again a few days after a reset
One reset restored heating and the same single blink returned within days.
The reset cleared the code and not the cause. A furnace that needs its flame sensing restored repeatedly is reporting on combustion, gas pressure, or grounding, and each of those needs the burner compartment opened.
One code, two histories
The technical FAQ gives two triggers for the same single blink: four ignition trials with no flame sensed, or four flame failures inside one heat call. Those clauses describe opposite events.
In the first the control ran its ignition sequence four times and never received confirmation of a flame, which points at gas arriving, the igniter, and everything the control checks before it opens the valve. In the second the burner lit on each attempt and the flame signal was lost, which points at the sensing circuit and at the conditions that weaken it.
The owner is the only person who can supply that distinction after the fact, because the code does not preserve it. Standing near the furnace through one lockout sequence and noting whether the burner is audible is worth more than anything else you can do before calling.
What Rheem attaches to a failed flame signal
Three causes appear in the FAQ and only one of them is the sensor itself. Supply polarity and phasing appear first, deposits on the rod second, and manifold gas pressure third.
Polarity is the one that surprises people, because it is a statement about the electrical supply rather than about the furnace. Flame rectification relies on current returning through the grounded burner assembly, so a supply wired the wrong way round or a poor ground breaks a circuit that has nothing visibly wrong with it.
Manifold pressure works through the flame itself. A flame that is too small may not properly envelop the sensing rod, and Rheem separately links excessive manifold pressure to overheating and the main limit opening, which is a different symptom arising from the same adjustment.
The reset, and what it costs to repeat
The published clearing method is short and deliberate: cut the 115 volt supply, or the thermostat, for a count of five to ten seconds. It is a power interruption rather than a waiting period.
The furnace will then run its ignition sequence again from the beginning, and if the cause is still present it will reach the same lockout after four more attempts. Nothing is learned by that, and each cycle sends unburned gas into the heat exchanger four more times before the valve closes.
Reset once after establishing what you observed. If the lockout returns, the useful next action is a service visit with the observation attached rather than another attempt.
Why the pressure switch does not belong under one blink
The same Rheem FAQ gives pressure-switch conditions their own LED patterns: two blinks for an open switch and four blinks for a closed switch. That makes the blink count a boundary between separate diagnoses.
A pressure switch can prevent the sequence from reaching ignition, but a confirmed one-blink lockout records failed ignition trials or flame failures. It does not authorize relabelling the event as a pressure-switch fault.
If the pattern is two or four blinks, record it without bypassing or manipulating the switch. Combustion-air and venting checks belong to a qualified technician and the exact furnace service literature.
The ignition sequence has stages, and the stage the furnace reached on each attempt separates the two halves of the one-blink code.
- Inducer startsDraft is established before anything else happens
- Safety sequence completesPressure-switch faults use separate two- or four-blink patterns
- Igniter and gas valveReaching this stage without a burner sound means no ignition
- Flame signal confirmedA burner that lights and dies failed here, four times
What to give the technician
Tell the technician whether the burner was audible on each attempt, how many attempts you counted, whether the inducer ran, whether other gas appliances work, what the filter looked like, and whether a reset restored heating and for how long. Give the model and serial number printed on the rating plate as well.
Safe homeowner checks
- Stand where you can hear the furnace and note whether the burner is audible on each attempt before the lockout.
- Count the blinks and confirm the pattern repeats rather than changing between cycles.
- Check that other gas appliances in the house work, without operating a valve or opening the furnace cabinet.
- Confirm the filter is clean and every supply register is open, since airflow faults produce a different code.
- Clear the lockout once, by interrupting the 115 volt supply or the thermostat for a count of five to ten seconds.
Is a reset appropriate?
The published clearing method interrupts the 115 volt supply, or the thermostat, for a count of five to ten seconds. One attempt after you have observed and recorded the sequence is the whole of the useful allowance, because a cause that is still present produces the same four attempts and the same lockout.
When to call a technician
- The same lockout returning after one reset with the gas supply confirmed.
- A two-blink or four-blink pressure-switch pattern, which is a separate combustion-safety service path.
- Any work on the flame sense rod, gas valve, or manifold pressure, all of which need the burner compartment opened.
- Suspected supply polarity or grounding problems, which are electrical rather than heating work.
- Any smell of gas, which is an evacuation and an emergency call rather than a service request.
Questions people ask about this
What does one blink mean on a Rheem furnace?
The published meaning covers two events: no flame sensed across four ignition trials, or four separate flame failures inside one heat call. Which of the two occurred is not recorded by the control.
How do I reset a Rheem furnace lockout?
Interrupt the 115 volt supply, or switch the thermostat off, for a count of five to ten seconds. That is a power interruption rather than a timer being waited out.
Why does the furnace light and then shut off?
That is the flame failure half of the code. The three causes the FAQ attaches to it are supply polarity and phasing, deposits on the sense rod, and manifold gas pressure set outside specification.
Can wiring polarity really stop a furnace lighting?
It appears in Rheem's own cause list. Rectification depends on current returning through the grounded burner assembly, so a supply or ground problem breaks a circuit that has no visible fault in it.
What if the furnace never even tries to light?
Record whether the igniter glows or sparks and whether a gas-valve click occurs. Four trials without flame are one half of Rheem's one-blink code, but the code does not identify the failed component. A pressure-switch condition uses a separate two- or four-blink pattern.
How many times can I reset it?
Once, after you have observed and recorded what happened. A cause that is still present produces the same four attempts and the same lockout, and repeated cycles add no information.
Evidence recordHow this page was checked
official manufacturer support article, service manual · checked 2026-09-08
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Rheem and Trane technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- official manufacturer support article, service manual
- Scope of the definition
- Rheem residential gas furnaces covered by the published technical FAQ
- Last checked
- 2026-09-08