How to Check a Flame Sensor on a Furnace Yourself
You're probably here because your heat just kicked away, and you're trying to figure out there how to check a flame sensor on a furnace before calling within an expensive maintenance tech. It's a classic winter disappointment: you hear the furnace click, the inducer motor begins humming, you observe the glow associated with the igniter, as well as for a glorious three seconds, you experience a puff associated with heated air. Then— click —everything goes cold again. It's enough to make anyone need to pull their own hair out, especially when it's 10 degrees outside and the house is cooling down fast.
The good thing is that the flame sensor is a single of the most common culprits with regard to this specific "short-cycling" behavior. It's a tiny, simple element that serves a massive safety purpose. Its job is usually to tell the control board, "Hey, there's actually a fire here, so keep the gasoline flowing. " If it's dirty or even broken, it can't send that indication, as well as the system shuts down to avoid your house from filling with unburned gas.
Symptoms Your Flame Sensor Is Acting Up
Before you begin having panels off, a person want to become reasonably sure you're looking at the particular right part. Usually, if the flame sensor is the particular problem, the furnace should go through its startup sequence just fine. You'll listen to the fan, notice the flames light up, but they'll go out almost immediately—usually inside five to 10 seconds.
If your furnace doesn't even try to light, or even when the igniter doesn't glow, you may be looking at a different problem, like a bad hot surface igniter or a stress switch problem. Yet if it lighting and then quits? That's the traditional "I can't view the flame" symptom. Sometimes you'll even see a specific mistake code blinking on the control board's little LED lighting. If you appear at the graph on the back from the furnace door, it may say something like "Flame sense lost" or "Low flame signal. "
Getting Ready with regard to the Job
You don't require a massive tool kit for this. Most of the period, you simply need a 1/4-inch enthusiast driver or a little socket set. A flashlight is also pretty much mandatory because furnaces are notoriously dark inside.
Initial things first: Safety. I can't stress this enough—turn off the strength to the furnace. There's usually a light switch-looking point on the part of the furnace or on a nearby wall. Turn that to "off. " If a person can't find this, go to your circuit breaker panel and shut it down there. You're going to become reaching around electrical components, and getting a zap is a quick method to ruin your own day. You should also turn the gas control device to the "off" position just to be extra safe, though it's not strictly necessary in case the power is usually dead.
Finding and Removing the Sensor
When the power is off, pop the top panels off the particular furnace. You're looking for the burning assembly. The flame sensor is usually located on the opposite side of the burners from the igniter. While the particular igniter is often a flat or even cylindrical piece that will glows bright orange, the flame sensor is a basic, thin metal fishing rod, often with a slight bend with the end, enveloped in a ceramic insulator. It'll possess a single wire (usually white or even yellow) plugged into the bottom of it.
It's usually held in simply by one lone screw. Go ahead plus unplug the wire—it's just a spade connector, therefore it ought to slide right off—and then back away that screw. Become careful not to drop the screw into the darkish abyss of the furnace cabinet; obtaining a dropped mess in there is similar to looking for a needle in a haystack.
The particular Visual Inspection
Once you've got the sensor within your hand, take a good view it. If it's covered in a level of black soot or a white, powdery oxidation, that's your problem. Over time, the burning up gas leaves behind a thin film associated with carbon and silica. This film functions as an insulator.
Consider it like this particular: the flame sensor works by a process called flame rectification . It actually utilizes the fire by itself to conduct a little bit of electricity. When that metal pole is coated within "gunk, " the particular electricity can't leap from the pole in to the flame, and the furnace thinks there's no fire.
Check the ceramic component too. When the white ceramic insulator is cracked or wiggly, the sensor will be toast. A split can cause the electricity to leak out to the particular metal frame of the furnace (shorting it out) instead associated with dealing with the flame. In case you see a crack, don't also bother cleaning it; you just need to to purchase a new one particular. They're usually very cheap, often under $20.
How to Check a Flame Sensor on a Furnace along with a Multimeter
If the sensor looks relatively clean but the furnace still isn't operating, you may get a little bit more scientific. To really know if it's doing the job, you'll want a multimeter that will can read microamps (usually denoted as µA). This is the "pro" way to do it.
To do this particular, you actually possess to put the particular sensor back within and hook your meter up "in series. " This sounds complicated, yet it just means the electricity provides to flow via your meter on its way from the sensor to the control panel.
- Link one lead of your meter to the spade connector on the flame sensor.
- Connect the other lead of your meter to the particular wire you originally unplugged from the sensor.
- Established your meter to the DC Microamps (µA) environment.
- Turn the particular power back on and start the furnace (be cautious, the panels are usually off and the particular parts are moving).
When the flames kick on, appear at your meter. Most furnaces desire to see a signal between 2. zero and 6. zero microamps . If you're seeing something really low, such as 0. 5 or 0. 8, the sensor is possibly still dirty or failing. If a person see 0. 0, the sensor is completely dead or even there's a burglary the particular wire.
Cleansing the Sensor the Right Way
If the sensor is just dirty, a person can usually fix it in about two minutes. You desire to use some thing mildly abrasive. Steel constructed from wool or even a piece of emery cloth works best. I've seen people use sandpaper, but you have to become careful with this. When you use a very coarse sandpaper, it could leave serious scratches that really collect more soot faster the next time. Definitely avoid using a wire brush or anything with large oils on this.
Just provide the metal pole a light scrubbing up till the metal looks bright and sparkly again. You don't need to move crazy; you're simply trying to remove that invisible level of oxidation. Once it looks clean, wipe it away from with a dried out paper towel to make sure there's no dust or oil out of your fingers still left on it. Don't touch the metal rod with your own bare hands after you've cleaned this, as the oils from your epidermis can actually "cook" on to the rod and start the buildup process all over again.
Putting Everything Back again Together
Glide the cleaned (or new) sensor back into its hole, tighten that screw down, and plug the wire back in. Make sure the particular wire is tight. If the spade connector feels unfastened, you can give it a small squeeze which includes pliers to make certain this makes a strong connection.
Put the furnace doors back on. Most modern furnaces have a safety change (a "door switch") that won't allow the furnace run if the -panel is off. In case you try to test it with the doorway off, nothing will happen, and you'll think you got destroyed something.
Flip the power back on, turn the gas back on if you shut it off, and crank up the particular thermostat. If the furnace stays lit for more than 30 seconds, you've officially won.
When Washing Isn't Enough
Sometimes, you may clean a sensor until it shines like a diamond and the furnace still won't remain lit. If you've cleaned it and you're still obtaining that short-cycling, it might be a grounding issue . Since the flame sensor relies on the furnace body being grounded to complete the signal, a loose surface wire anywhere within the system may mimic a poor flame sensor.
Check the particular burner assembly itself. If the burners are super rusty or corroded exactly where they bolt to the furnace, the "path" for the electricity may be blocked. Sometimes just loosening and re-tightening the particular screws that hold the burners in place can refresh that will ground connection.
At the end of the day, learning how to check a flame sensor on a furnace is one of all those "homeowner wins" that will saves a $150 service call regarding what is essentially five minutes associated with cleaning. It's a great piece of DIY knowledge to have in your back pocket for once the temperature drops as well as the furnace starts acting finicky. If you clean it and it still doesn't work, a minimum of a person can tell the particular technician, "I've already checked the flame sensor, " which might save them several diagnostic time—and help you save some money.