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jhager1979

join:2013-02-13

Conquest 80 flame sensor

Ok, so I've dealt with this problem before but had someone else fix it. Different house, different furnace, so I'm not familiar with this thing. I'm a pretty handy female, but messing with a furnace makes me a little nervous. I know it is a flame sensor because of what it's doing. The problem is I don't know what it looks like or where it is so I can clean it off. Where the heck is this thing? Please help. 20 degrees and have a 6 month old baby and the house is getting cold fast.


cowspotter

join:2000-09-11
Ashburn, VA
kudos:2
Look for a "stick" that is in front of one of the burners in the furnace. It will be in the path of the flame once the burner is lit. I believe it should be in front of the burner furthest away from the ignitor/pilot.

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:2

1 edit
reply to jhager1979
said by jhager1979:

messing with a furnace makes me a little nervous ... have a 6 month old baby and the house is getting cold fast.

I sincerely suggest you call someone to come prepared with a new flame sensor.

Google image search will show typical thermocouple flame sensor and variations like infrared. If you really want to clean it first by yourself, please turn off the heat at the thermostat and also turn off the furnace switch/breaker.

P.S. Stay around while they check/fix the furnace because I had a bad experience recently where a guy whacked the heat exchanger while I was not looking and asked me to replace the whole furnace.

patcat88

join:2002-04-05
Jamaica, NY
kudos:1
reply to jhager1979
Why do you need to clean it off? Its natural gas. The flame sensor might not be the problem. Your flame or chimney could be the problem. Disabling the flame sensor or "fixing" it to work will just fill your house with CO and everyone dies.


SparkChaser
Premium
join:2000-06-06
Downingtown, PA
kudos:4
Reviews:
·Verizon FiOS
said by patcat88:

Why do you need to clean it off? Its natural gas. The flame sensor might not be the problem. Your flame or chimney could be the problem. Disabling the flame sensor or "fixing" it to work will just fill your house with CO and everyone dies.

Ii have electic heat so this is based on my son's house. The flame sensor on his gas furnace gets dirty and needs cleaning/replace every couple of years. As part of maintenance it gets cleaned.
--
--
--
"Facts do not cease to exist because they are ignored." - Aldous Huxley


dark_star

join:2003-11-14
Louisville
kudos:1
reply to jhager1979
I do not recommended this as a do it yourself job. If you mess up, you could blow up your home, burn down your house, or kill your entire family with Carbon Monoxide gas.

Going to proceed anyway?

Then do a Google image search for “flame sensor”. You'll get photos of typical flame sensors and their placement.

Turn off the thermostat.

Turn off power to the furnace, air conditioner (if equipped with central air) and blower at the circuit breaker box.

Remove the burner cover from the furnace.

Take a very small piece (literally, the size of a postage stamp would suffice) of very fine sandpaper, wrap it around the metallic portion of the flame sensor, and supplying moderate fingertip pressure slide the sandpaper from base to to tip. Give it three strokes. No more.

Wipe the newly sanded flame sensor with a lint free rubbing alcohol dampened cloth. If your furnace has a pilot light, omit the alcohol and use water dampened cloth instead. Remove alcohol container and cloth far from the furnace.

Replace cover, and restore power.

I did the above procedure to my furnace when it quit working the night of January 1st, 2009. It has been working fine ever since. After that, I did buy the following spares for about $50: flame sensor, igniter, flame roll out sensor.


cowspotter

join:2000-09-11
Ashburn, VA
kudos:2
Do not use sandpaper. Use emery cloth


CylonRed
Premium,MVM
join:2000-07-06
Bloom County
reply to patcat88
said by patcat88:

Why do you need to clean it off? Its natural gas. The flame sensor might not be the problem. Your flame or chimney could be the problem. Disabling the flame sensor or "fixing" it to work will just fill your house with CO and everyone dies.

Because it needs to be done - even with nat gas... Should be pretty rare but indeed - they do need to be cleaned - even with nat gas.
--
Brian

"It drops into your stomach like a Abrams's tank.... driven by Rosanne Barr..." A. Bourdain

jhager1979

join:2013-02-13

1 recommendation

reply to jhager1979
Thanks everyone for your help! Found the flame sensor in the exact spot "cowspotter" said it would be. I also followed "dark_star" cleaning instructions with water and "cowspotter" emery cloth. Also changed filter. Works great now! Thanks to everyone else for your concerns and suggestions.


tp0d
yabbazooie
Premium
join:2001-02-13
Carnegie, PA
kudos:6
NEVER use anything sand based to clean something that will get hot enough to melt said sand. (ie a flamerod) Melted sand (glass) is an insulator and can actually make the problem worse.

Always use either a knife or steel wool to scratch away buildup and expose fresh steel.

-j
--
if it aint broke, tweak it!!
currently on FiOS (kick aZZ!)


rockotman
...Blown On The Steel Breeze
Emerging Research
join:2000-08-06
DSotM
kudos:2

1 edit
reply to jhager1979
I had to clean the sensor in gas furnace in my previous house about once every two years.

As tp0d said, with steel wool.

With mine, you actually had to remove a small sheet metal screw to get the sensor out away from the burners so that you could clean it.

But as posted above, secure all power to the furnace, remove the burner cover, and gain access to the sensor.

This is what the sensor in my Carrier furnace looked like (yours should look somewhat similar, perhaps straight, perhaps shorter, but generally a metal rod with a connector for a wire at one end.

.
The screw I mentioned above when through the hole that you can see in the base of the sensor. The area that required cleaning is toward the tip on the left side of the photo. No need to disconnect that wire while cleaning, unless you need to do so to get it into a position to clean it.

One other question... is there a small window on the furnace through which you can see a flashing red LED? If so, the series of flashes are spelling out a code. The code usually can be deciphered by looking at a chart or instruction sheet glued to the inside of the cover of the furnace. The pattern of the flashes translate to an error code that can be read off of this sticker.

If this has been occurring to the point that the furnace is not turning on or even trying to turn on at all, the code being flashed may decode to a "lock-out" condition. This can be caused by several different things, but is usually the result of some error being detected three consecutive times. It causes the control system to lock out to keep from retrying to start the faulted furnace. One of the most common causes of the lock-out is three consecutive failures of the flame-proving circuit; the sensor is part of that circuit.

Securing and then restoring the power to the furnace will generally clear a lock out condition. If the fault recurs, the LED will begin flashing again, this time with a different pattern. This pattern is the fault that is ultimately resulting in the lock-out condition after three consecutive failures.

With my Carrier furnace, sometime just securing and restoring the power would get the furnace going for a few more hours until I got a chance to get in there and clean the sensor. This was a handy tip for my wife when it occurred when I was out of town one year.
--
Shine on you crazy diamond...

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:2
reply to tp0d
Click for full size
said by tp0d:

NEVER use anything sand based to clean something that will get hot enough to melt said sand ... Always use either a knife or steel wool to scratch away buildup and expose fresh steel.

The sand melting into glass part makes sense but using a knife, exposing fresh steel, sort of goes against professional advice to be really gentle on the flame sensor

It is very IMPORTANT not to use anything too abrasive on the metal part of the flame sensor. A soft Brillo pad, steel wool, or very very fine sand paper should work. If you don’t have any of those you may be able to use a dollar bill as a quick substitute.

In that photo, they are using fine grit sand paper but even emery cloth could leave minute residue which could melt in the flame. Maybe cleaning afterwards with a lint-free cloth would be a good idea.


tp0d
yabbazooie
Premium
join:2001-02-13
Carnegie, PA
kudos:6
Gentle? Why? its a chunk of steel... I`ve heard tales of a "coating" or etc.. but what coating stands up to a 2700F flame?

give me a good reason to be 'gentle'

-j
--
if it aint broke, tweak it!!
currently on FiOS (kick aZZ!)


Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4
reply to lutful
It is simply a piece of metal used as an electrical conductor. Scrapping it with a knife will not hurt it, some of my coworkers do it this way.

I use open mesh type sand paper. Clean and wipe the sensor after you are done with the paper. I've never had an issue with "making glass" after doing so, in many years servicing machines.

lutful
... of ideas
Premium
join:2005-06-16
Ottawa, ON
kudos:2
said by Lurch77:

It is simply a piece of metal used as an electrical conductor. Scrapping it with a knife will not hurt it, some of my coworkers do it this way.

The flame ionization process is very finicky. If you rough up the rod too much the flame amplifier circuit could see 10 microamps (just for example) instead of expected threshold of 20 microamps and falsely deduce that there is no flame.

P.S. Most often the problem with a flame rod will be some carbon (soot) or even tiny cracks on the insulator which reduces or kills the flame current.


CylonRed
Premium,MVM
join:2000-07-06
Bloom County
reply to tp0d
said by tp0d:

NEVER use anything sand based to clean something that will get hot enough to melt said sand. (ie a flamerod) Melted sand (glass) is an insulator and can actually make the problem worse.

Always use either a knife or steel wool to scratch away buildup and expose fresh steel.

-j

They guy who cleaned our sensor flat out said not to use anything to rough - he was very adamant about that. He said the emery cloth was perfect and was as rough as he would go. They would know better than me and I can only bet that what lutful said is very true.
--
Brian

"It drops into your stomach like a Abrams's tank.... driven by Rosanne Barr..." A. Bourdain


Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4
reply to lutful
said by lutful:

said by Lurch77:

It is simply a piece of metal used as an electrical conductor. Scrapping it with a knife will not hurt it, some of my coworkers do it this way.

The flame ionization process is very finicky. If you rough up the rod too much the flame amplifier circuit could see 10 microamps (just for example) instead of expected threshold of 20 microamps and falsely deduce that there is no flame.

I've never had that problem. I take readings every time I service a flame sensing device.


tp0d
yabbazooie
Premium
join:2001-02-13
Carnegie, PA
kudos:6
reply to lutful
said by lutful:

said by Lurch77:

It is simply a piece of metal used as an electrical conductor. Scrapping it with a knife will not hurt it, some of my coworkers do it this way.

The flame ionization process is very finicky. If you rough up the rod too much the flame amplifier circuit could see 10 microamps (just for example) instead of expected threshold of 20 microamps and falsely deduce that there is no flame.

P.S. Most often the problem with a flame rod will be some carbon (soot) or even tiny cracks on the insulator which reduces or kills the flame current.

Dunno what you've seen that runs on 20uA, but 99% of the equipment I work on uses a 0-10uA range, the veritable Honeywell 8600 series, for example. Most all controls prove at 2-4uA

as for cleanin, i do what works for me.. thats all you can do.

-j
--
if it aint broke, tweak it!!
currently on FiOS (kick aZZ!)