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Furnace Blinking 8 Times: What It Means and How to Fix It
Eight blinks is a furnace blink pattern that is easy to confuse with a furnace that never lights, but it means something more specific: the flame was established and then lost, over and over. On York furnaces it means the flame was lost five times during one heating cycle, on Trane furnaces it means a low flame sensor signal, on Goodman furnaces it means an igniter circuit problem, and on Lennox ML193UH furnaces it means a flame dropout lockout. The homeowner job here is chart first and hands off: read the chart inside your blower door, work the external checks in this guide, run one power reset, and hand the exact pattern and brand meaning to a technician, without opening the burner compartment, touching gas parts, or testing mains wiring.
Why this happens
Eight blinks is a flame dropout code on most brands that use a single blink count, and dropout is different from a furnace that never lights at all. Dropout means the burners did light, the flame sensor proved the flame, and then the flame was lost partway through the heat cycle, over and over. On York furnaces, eight red blinks means the flame was lost five times during one heating cycle, after which the board locks the furnace out for about 60 minutes. On Trane furnaces, eight flashes is the low flame sensor signal: the sensor is reporting a flame too weak to trust, which can come from a coated sensor, low gas pressure, or a burner that is not burning cleanly. On Goodman furnaces, eight flashes means an igniter circuit problem, a cracked or failing igniter, or an igniter that is not connected properly, so ignition itself is unreliable. On Lennox ML193UH series furnaces, eight flashes is also a flame dropout lockout after too many flame losses. The common thread is a flame the board cannot keep proving, and the homeowner checks are the same in every version: the door chart, the filter, the vent terminations, the ignition pattern you can hear from outside, and one power reset. Anything inside the burner compartment, including the sensor, the igniter, and the gas valve, is professional work.
Finding the cause
The door chart decides what 8 blinks means on your furnace
This is the first check and the one that makes the rest of the guide usable. Count the flashes carefully, note the pause between groups, and read the chart printed inside the blower door or on the back of the top door. York charts describe eight red blinks as flame lost five times during the heating cycle. Trane guidance describes eight flashes as a low flame sensor signal. Goodman charts describe eight flashes as an igniter circuit problem. Lennox ML193UH guidance describes eight flashes as a flame dropout lockout. If your chart says something else, your chart wins, and the checks below still apply in the same order, because filter, vent, ignition sound, and one reset are relevant to every version of the fault. If the chart is missing, faded, or unreadable, treat the meaning as unknown and call a professional rather than guessing from a brand table, since an igniter fault and a flame sensing fault are repaired by different tests and neither is a homeowner job. Write down the exact wording from your chart before calling anyone, because a technician who hears the brand meaning on the first call arrives with the right parts and the right tests.
A flame that lights and then drops out repeatedly is the dropout pattern itself
Stand near the furnace during a call for heat, with all access panels closed, and listen to the sequence. A flame that lights, burns for a while, and drops out, then lights again and drops out again, is the dropout pattern that eight blinks reports. That pattern fits the York flame lost five times version, the Trane low flame signal version, and the Lennox flame dropout lockout version, because in all three the board proved a flame and then lost it. This check is listen only, from outside the furnace. Do not open the burner compartment to watch the flame: the observation is for triage, not diagnosis, and the burner area holds hot surfaces and gas parts. Note how long the flame lasts each time and how many dropouts happen before lockout, because that timing separates a sensing fault from a gas pressure fault.
A furnace that never lights at all points to the Goodman igniter circuit version
A different sound pattern points to the Goodman version of eight blinks. If you hear the inducer start, but no flame ever appears, and the board reports eight flashes, the fault sits at ignition itself: a cracked or failing hot surface igniter, or an igniter that is not connected properly, so the gas never gets a reliable spark or hot surface to light from. That is different from dropout, where a flame appears and is lost, and the distinction tells the technician whether to test the igniter circuit first or the flame sensing chain first. The distinction matters only to the technician, who will test the igniter, the sensor, the valve, and the board in turn. Do not touch the igniter: a hot surface igniter is fragile, it breaks if handled roughly, and it sits among gas parts. One reset test after the external checks is the homeowner limit.
A dirty filter and a blocked vent termination can push a marginal flame toward dropout
Airflow checks belong in every furnace guide because a starved furnace burns badly, and a badly burning flame is exactly what a flame sensor struggles to keep proving. Hold the filter up to a light and replace it if light barely passes, using the correct size. Go outside and find where your furnace vents, a plastic pipe termination on a side wall on a high efficiency furnace, or a metal flue into a chimney on an older one, and look for snow piled against the pipes, ice at the openings, leaves, a nest, or a clogged screen, and check the intake pipe too if your furnace has one. Clear anything you can reach safely from the ground. This check matters because it is one of the few causes a homeowner can genuinely fix: if the code clears after a blocked termination is cleared and stays clear through a full heat cycle, the blockage was the story. If the termination was already clear, or the code returns, the fault is inside the furnace, and that is professional territory. Do not put anything into the flue, and never run the furnace with the vent knowingly blocked to keep the house warm.
Other gas appliances going weak at the same time points to gas pressure, not the furnace
A pressure fault announces itself across the house, and checking that takes two minutes with no tools. If you have other gas appliances, check whether a gas stove burner lights normally and stays lit, and whether a gas water heater is running normally. Burners that are weak, yellow, or will not stay lit, or a water heater that has also stopped, point to low gas pressure or an interrupted supply rather than a furnace part. Recent gas meter work, a shutoff for plumbing work, or an empty propane tank explains a sudden dropout lockout the same way. If the gas supply to the house appears to be off, or you smell gas at any point, stop troubleshooting, leave the house, and call your gas utility from outside. Never turn a gas meter valve back on yourself: restoring supply after a shutoff is utility work, and the utility will relight and check appliances.
Repeated power interruptions explain the York repeated recycle version of 8 blinks
York guidance also links eight blinks to ignition lockout after repeated power recycles, and that history check is worth making. Ask whether the power has flickered, whether breakers have tripped, or whether someone has been cycling the furnace power to clear another code. Repeated power cycling during ignition can leave the board counting flame losses that were really power losses, and it also hides the original fault pattern a technician needs to see. That history tells the technician to check power stability and the board, not just the burner parts. There is no homeowner test for this beyond the history itself: confirming it means testing inside the furnace, which is professional work with live voltage and gas parts. Report the power history exactly as it happened, including dates and how many times the power was cycled, and do not cycle the power again to test the theory.
| What you find | What it means | What to do next |
|---|---|---|
| Door chart says flame lost 5 times (York) and the flame drops out repeatedly | Flame sensing or gas pressure is failing partway through the cycle | Run one reset after the filter and vent checks, then call a professional if lockout returns |
| Door chart says low flame signal (Trane) and the flame is weak or short lived | A coated flame sensor, low gas pressure, or a burner not burning cleanly | Note the flame duration and call a professional for sensor and pressure testing |
| Door chart says igniter circuit (Goodman) and the flame never appears | A cracked, failing, or poorly connected igniter | Stop after one reset and call a professional, do not handle the igniter yourself |
| Door chart says flame dropout lockout (Lennox) after repeated losses | The board has counted too many flame losses in one cycle | Run one reset after the external checks, then call a professional if it locks out again |
| Other gas appliances are also weak or out | A gas supply or pressure problem affecting the whole house | Stop troubleshooting, call your gas utility, never turn a meter valve on yourself |
| 8 blinks persist with a clean filter, clear vent, and normal gas appliances | An internal fault remains: sensor, igniter, valve, or board | Call a professional for testing inside the cabinet |
Fixing it
- Record the pattern and read your door chart, about 5 minutes. Count the flashes and the pause, note whether the pattern repeats steadily, and copy the exact wording from the chart inside the blower door. If the chart is missing or unreadable, stop here and call a professional.
- Check thermostat, switch, breaker, and filter, about 10 minutes. Confirm the thermostat is set to Heat and above room temperature, the furnace power switch is on, the breaker is on, and the filter passes light when held up to it. Replace a clogged filter with the correct size.
- Check other gas appliances, about 5 minutes. See whether a gas stove burner lights normally and a gas water heater runs normally. If other gas appliances are also out or weak, stop here and call your gas utility. If you smell gas, leave the house and call from outside.
- Clear the outside vent or flue termination, about 10 minutes. Remove snow, ice, leaves, nests, or debris from the exhaust and intake terminations, working only from the ground and only from outside. Do not insert anything into the flue.
- Listen to one heat call, about 5 minutes. With all panels closed, listen for the inducer first, then ignition, then whether a flame lights and drops out repeatedly or never appears. Note how many dropouts happen before lockout, because that timing tells the technician which fault family to test first.
- Reset once and observe one full cycle, about 15 minutes. With no gas smell found, switch the furnace power off, wait at least 30 seconds, switch it back on, and watch one complete heat cycle from outside the furnace. On York and Lennox models the board may sit in a lockout period before it retries. If 8 blinks return at any point, switch the furnace off and call a professional. Do not reset a second time, and never open the burner compartment or adjust a gas valve to keep the heat on.
Reset and clearing
Switch the furnace power switch off, wait at least 30 seconds, then switch it back on. One power reset after the external checks is the safe homeowner test for every version of this code. On York and Lennox models the board may still sit out a lockout period before retrying, so a reset that does not produce heat at once is not proof the fault is fixed. An 8 blink pattern that returns after one reset, with a clean filter and a clear vent, is reporting a real fault inside the furnace or its gas supply. Do not keep cycling the power, do not open the burner compartment, and do not adjust gas parts to force heat.
What it costs
The free external checks are the cheap outcomes. Every internal version of this code is a professional repair, and the price spread below reflects how different the York, Trane, Goodman, and Lennox faults really are.
| Item | DIY cost | Part only | Fitted by a service |
|---|---|---|---|
| Clearing the vent termination and replacing the filter | $0 to $20 for a replacement filter | No part needed | Not applicable |
| Flame sensor replacement (Trane low flame signal version) | Not a homeowner job, sensor sits at the burners | $15 to $40 for the sensor (estimate) | $150 to $300 fitted, including diagnosis (estimate) |
| Hot surface igniter replacement (Goodman igniter circuit version) | Not a homeowner job, igniter is fragile and sits at the burners | $30 to $80 for the igniter (estimate) | $200 to $400 fitted, including diagnosis (estimate) |
| Gas valve replacement, if pressure testing points to the valve | Not a homeowner job, gas supply work | $150 to $400 for the valve (estimate) | $450 to $900 fitted, including diagnosis (estimate) |
| Control board replacement, if the board is the fault | Not a homeowner job | $150 to $450 for the board (estimate) | $400 to $800 fitted, including diagnosis (estimate) |
All prices on this page are estimates based on typical US parts and service pricing. Your model, region and the actual failed part will move the real figure.
Repair or replace note: a flame sensor, an igniter, or a gas valve repair is almost always worth doing, since each fitted cost is a small fraction of a replacement furnace. A control board repair on a furnace over 15 years old needs the heat exchanger checked first, because there is no sense fitting a new board to a furnace whose exchanger then fails inspection. A condemned heat exchanger almost always means a new furnace, typically $3,500 to $7,500 installed (estimate). The full pattern list is on the furnace blink codes hub, and the companion patterns are the furnace blinking 7 times guide and the furnace blinking 6 times guide.
Mistakes that make it worse
- Assuming 8 blinks means a furnace that never lights. Dropout means the flame appeared and was lost, which is a different fault family from a dead igniter. Listen to the sequence before deciding which version you have.
- Repeatedly resetting to keep the heat on. Each reset after a genuine fault lets the failure repeat and hides the dropout count a technician needs to see. One reset is the limit.
- Opening the burner compartment to watch the flame or clean the sensor yourself. The burner area holds hot surfaces and gas parts, and a disturbed sensor wire creates a new fault. Sensor and igniter work is professional work on this site.
- Handling a hot surface igniter yourself. Hot surface igniters are fragile and break if handled roughly, and a cracked igniter can fail intermittently. Igniter replacement is professional work.
- Adjusting a gas valve or its pressure screws. Gas valve adjustment changes the fuel supply to the burners and can create an unsafe flame or a gas leak. No homeowner adjustment is ever part of this code.
- Turning a gas meter valve back on yourself. Restoring supply after a shutoff is utility work, and the utility will relight and check appliances. A homeowner restart can feed gas to an appliance that is not ready for it.
- Running the furnace with a blocked vent to get through the night. A blocked exhaust disturbs the flame and is a carbon monoxide risk. Clear the termination or leave the furnace off.
Stop and Call a Professional If
- You smell gas at any point, or the carbon monoxide alarm sounds: leave the house and call your gas utility or 911 from outside.
- 8 blinks return after one reset with a clean filter and a clear vent.
- The flame drops out repeatedly, or never appears at all, after the reset.
- Other gas appliances are also weak or out, suggesting a supply or pressure problem.
- Your door chart says igniter circuit or low flame signal, or any work would involve the igniter, flame sensor, gas valve, control board, heat exchanger, or mains wiring.
- Your door chart is missing or unreadable, so the meaning of the pattern is unknown.
Never work on gas lines, burners, heat exchangers, or inside electrical panels. Never bypass a safety switch. If anything in this guide conflicts with your model's manual or a safety warning on the furnace, the manual and the warning win.
Frequently Asked Questions
Does 8 blinks mean the same thing on every furnace?
No. Eight blinks means flame lost five times on York furnaces, a low flame sensor signal on Trane furnaces, an igniter circuit problem on Goodman furnaces, and a flame dropout lockout on Lennox ML193UH furnaces. Other brands vary again, so the chart printed inside your blower door is the only reliable source for your model.
What is flame dropout?
Flame dropout means the burners lit and the flame sensor proved the flame, and then the flame was lost partway through the heat cycle. When the board counts enough losses in one cycle, five on York models, it locks the furnace out rather than keep relighting an unreliable flame.
Can I fix an 8 blink code myself?
The homeowner part is diagnosis and external checks only: read the door chart, check the filter and the outside vent termination, check other gas appliances, listen to the ignition sequence, and run one power reset. Flame sensors, igniters, gas valves, wiring, and control boards are all professional work, because they sit at the burners, the gas supply, or the mains wiring.
Related Guides
- Furnace Blinking 7 Times: What It Means and How to Fix It
- Furnace Blinking 6 Times: What It Means and How to Fix It
- Furnace Blinking 5 Times: What It Means and How to Fix It
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