Wake up this morning, all the kids are still in bed.  Go wake them up and I get - it's cold, can i sleep in another 10 mins.
Hummm.... you're right, it is a bit cold.  I go check the thermostat, 59 degrees.  Crap, the furnace is out.  Check the time on the air filter on the thermostat.  No plenty of time left (last time I didn't change the filter, got a low air flow fault).  Reset the system, look at the LED to read the error codes.  You will have a little LED flashing, count the number of flashes, find and read what the flashes correlates to.
The wheel in the blower turns, hear the click in the gas valve go but no glow.  Dang Hot surface ignitor in my force air furnace went.  The system couldn't start so it locks out for three hours because of the fault.

Call up my neighbor who's a commercial HVAC guy, have him order me TWO (2) igniter for me to pick up since most supply houses doesn't service non commercial accounts.  45 mins later, I drive home with the part, swap out the bad one and install the new one.  Reset the furnace, igniter glows red, NG hits it and wam I'm back in business.  Igniters are usually very accessible.  Held in by one to two screws.
Look at the right side by the last burner.

PSA to GD, always have a spare Igniter on hand for the model of furnace you have in your home.  They only cost $20 to $40.  To get the right part for your furnace just get the Make and Model info and you can order it online, unless you're like me and caught without one when it breaks and needs it right now this instance.
You don't have to mess with splicing wires as they have a plastic connector on the end.

A bad igniter looks like this.


Another style ignitor looks like this.

Goldenlight is right, this could be a thermocouple

If you were to call this in for service.  You're paying someone to make a
house call $100 plus parts.  Mark up on these parts are usually 75% and
up.  You could be out easily $200+ for a 10 minute job.
ALSO DON'T TOUCH THE ELEMENTS ON THE NEW ONE, the oil on your hands can and will ruin it and reduce the life of the device.
 

thats fine if you wanna fix your own stuff, but you dont have to be insulting.  how about i call your boss and tell him how easy your job is and that any idiot could do it?

Not just the oil n your hands.

I had one of those lint traps which goes on the end of the dryer vent hose, which allows you to vent the clothes dryer inside for added humidity in the wintertime. I kept having to replace my flame sensor (which looks like the second example you posted) about every two months. It was making me crazy -- I thought it was a run of defective parts.

I mentioned this to a friend who owns an HVAC business. He told me that the vapors from the clothes dryer, because they had traces of fabric-softener in them, were coating the flame sensor and preventing the igniter from firing. Sure enough, simply wiping the flame sensor off with a paper towel and acetone got everything running again.

I cleaned the other three flame sensors I had replaced, by wiping them down with acetone and a clean paper towel. All of them worked properly again when I swapped them back into the furnace.

I now have my dryer vented outside year-round, and a lifetime supply of flame sensors.

Another quick trick if you don't have a spare handy and the ignitor isn't broken is to give it a very light going over with a scour pad or very fine sandpaper.  Reinstall and they usually light right up, just a little carbon built up on the legs.

Order online BEFORE it goes out.  



Just like a thermocouple, having one on hand beats waiting for the parts store to open.  BTW, there are a few parts places that sell to ordinary peons.


 

Most fail by fracture.  They are silicon carbide, a brittle ceramic.  Thermal stress kills them



 

Yep, had an igniter go south on me on a friday night on a holiday weekend once.

Its when i really learned the one is none, two is one mantra.

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A'yup, it seems like every year, an igniter goes bad on my mom's furnace.

There is also another doo-dad, a thick metal wire that is somehow able to detect electrical current flow through the flame.  I guess it is what tells the furnace's computer to keep pumping gas to the burner.

I've been told the igniters are ceramic, so you have to be kinda gentle with them.

Didn't mean to sound insulting.  Just wanted to save folks a few dollars in these hard times on a simple job most people who are inclined can do.  I'm not telling people to break out the bernzomatic to sweat joints.





As for my job, yea, a trained monkey can do it.  It's just a console into a switch / router.



I'll even give you a glimpse of it.









 

Outstanding!





 

Bingo



 

Flame sensor.  It will shut off the gas if no flame is detected.



 

Nice writeup!   I spent a night sleeping in a mummy bag by the gas fireplace when my igniter went out during a serious cold snap.

And, yes- you bet I ordered a spare.  I am not doing that again!  

Right on!



 

same thing happened to me a month ago. easy quick cheap fix.

Holy shit, you're still using 3640's? I have one on my desk collecting dust that was handling RAS via ISDN ages ago.

Nah, just needed a pic.  I'm currently stuck on a ASA 5585.  Most of my edge stuff are 3650X.  I leave the Nexus stuff for the hard core folks.



eta - good eye.  i've seen folks who post their console screen with their password on the configs, lol.  Gotta love IOS.





 

In 17 years I have replaced 2 igniters, a motherboard and now I have a failing pressure switch in our gas furnace.

Already have a spare igniter and motherboard. Time to order a couple of pressure switches.

Just had a similar issue, ignitor lit pilot, but main burner wouldn't come on. Turned out pilot tube was partially blocked, so flame was hitting sensor, but not enough. Had me looking at all kinds of stuff. It was a Honeywell smart valve. If pilot lights, but main burner doesn't, and ignitor stays activated, there's not enough flame to activate the flame sensor.

Good for you on fixing it on the cheap. I replaced a pc board on my unit for 89 bucks shipped when several different repair men wanted between 1200 and 1500 bucks to get my heat back on.

Good for you on fixing it on the cheap. I replaced a pc board on my unit for 89 bucks shipped when several different repair men wanted between 1200 and 1500 bucks to get my heat back on.

Good for you on fixing it on the cheap. I replaced a pc board on my unit for 89 bucks shipped when several different repair men wanted between 1200 and 1500 bucks to get my heat back on.

Nice work.  Save your $$$ for the family and guns & ammo.



 

If you know how your HVAC system goes through its cycles it pretty easy to know when HSI is bad.

I've fixed mine once and a buddies, it seems to be the most common thing to go out on these systems.

Yeppers, always have one on hand and don't make the same mistake I made.



 

you are thinking of the flame sensor.

BTW-- my POS of a furnace (goodman) goes thru these like water...or something...
i have replaced it like 8 times...thise swqugily ones like you got SUCK  They make a FLAT one piece one that lasts WAY longer.

mine is buried ass deep in my furnace too---gotta take it all aprt to get to it.

Yuck.





 

Back to 72 degrees.



No more complaining it's cold by the kiddies.  Only if I can get them to turn off the lights when they leave a room.

Thanks for joining in on a fun day.



Good night!

I just replaced the fuel pump and transformer in my fuel oil furnace. Being able to work on your own furnace is a big plus.

FYI if it's really cold out you can manually light your furnace even if your HSI goes out. And when the flame sensor starts being flakey I have had good luck with using a 100 dollar bill like sand paper to clean it up.

T

My house has two furnaces (one upstairs, one down) and I address one about every year with this issue. Very simple repair. I once called an HVAC tech to do the same thing and he charged me just south of $300.



This year I also had one of my gas valves go bad. I ordered that online as well (~$70 part) and replaced it myself. Used the thicker / yellow 'teflon' gas tape to seal everything up, and it works like a charm.



Yes I sort of feel bad that the gas man isn't getting the business, but our house budget is pretty damn tight as it is, cant spare $$$ for constant repairs.

Clean it with a green scotch pad or fine emery paper. That rod uses the burner flame as a path to send electricity back to ground and the board so the board knows the burners are lit and keeps power on to the gas valve.

If you just want a spare igniter, buy a "Firefly" it'll work on most furnaces that don't have some funky attachment setup.

I didn't try it, but I was told I can manually light it with a benzomatic when the gas valve opens.  Not sure if there's a sensor that detects an incomplete circuit in the ignitor though.



 

Some furnaces [modular/trailer Coleman Evcons for example] do use the igniter as a flame sensor. They will be a round spiral wound igniter.

Good to know, thank you!



 

The HSI in my oven uses the current as a trigger for the gas valve.  When the HSI is starting to fail, the trigger current rises slower so the gas valve opening is delayed.  Then I know it is time to replace it.  But this is an older oven, anything with a flame detector can be lit manually.  



 

That is REALLY good information, and the pictures are top notch; many thanks.



That last picture sure looks a LOT more like a thermocouple, than a flame igniter.



The wires are very small gauge, and insulated with plastic, instead of a heat resistant material.



I could easily be wrong; I'm far from an expert, but I have replaced a couple of thermocouples, that looked similar, but not the same as your picture.



A thermocouple is also something it's a really good idea to keep on hand, as they fail without warning and will shut down a furnace, gas drier or water heater that depends on a pilot flame for ignition.



The simplest repairs are the most common, and probably 60 - 70% of gas furnace, gas water heater, and gas drier failure to heat are due to thermocouple and igniter failure. As the OP said the repair bill is very expensive.



The first time you do one will take more than 10 minutes, but it's only difficult because you've never done it before. The next time will seem easy, believe me.


 

I've checked up on HVAC technicians a couple of times and found out that they (the ones I checked on, anyway...) were charging 200%-400% markup on parts.

$12 A/C capacitor charged $48

$15/lb refrigerant charged $65/lb

$50 "hard start kit" charged $98

PLUS service call PLUS $100/hourly rate.

I wonder how many dope dealers study HVAC repair in voc-rehab in prison. The profits are better than Pablo Escobar got on coke.

You're right the last one it could be a thermocouple.  I found another image of a HSI.  Since there are different designs.





btw, question for anyone actually, if you have an HSI, you don't have a thermocouple correct?  Because either would be the ignition source.  My gas fireplace has a thermocouple.





Why the different designs?



 

It's all about the convenience.  I understand the cost.  Most people won't touch their appliances to repair them.  So you can mark it up according to what the market will bear.



It's also a PITA business just ask Drfrige.





 

This. I wouldn't sell the shit from my septic tank for 75% markup. Everything is 200-400 percent or more on certain items. Any less and I can go work a job somewhere for that much. You're paying for convenience, overhead, office people and lots and lots of pent up frustrations that we have dealing with the public all day.

Customers make me hate my life sometimes.

edit - customers make me hate my life every day. decent pay is the only thing that keeps me going.

Sig line material right there, lol.