Flame Sense rod questions

[novice 39]

Hello all,

My ICP Comfortmaker furnace is well maintained (even the blower bearings are oiled!!), and I am extremely happy with its dependability, but every couple of years, it develops a false start problem, and its always the same reason -- the flame sense rod has finally become dirty. A quick cleaning with fine steel wool, and everything's great again. I do have some curiosity-type questions however:

1. What exactly is the material building up on the rod? Is it just normal byproducts of combustion of natural gas? Or is it an indicator of some type of impurity in the gas/air?

2. Is the flame sense rod solid all the way through, or is it plated with some special metal (and will I eventually wear through that metallic plating?)

thanks,

novice 39

[tinknocker service tech]

a combanation of everything
as long as the the porsilan isnt cracked steel wool wont hurt
the rod is solid

[novice 39]

Thanks tinknocker!

I had read up on flame rectification (cool stuff!) but had never seen any info on whether there were any special properties of the rod itself.

If only igniters were as tough... that's the only other thing that has ever needed replacement on this furnace, which is understandable considering the environment they operate in.

thanks again

[precise temperatures]

Steel wool is correct to use, not sandpaper, but to be honest with you I have never offered this to a customer. I am in the repair business, not in the "temporary" repair business and to protect myself from callbacks that I cannot charge back to someone - either customer or manufacturer, I will not just clean it up and hope it works.

And to comment on what causes them to go bad, oxidation will form on them from the by-products of the fuel being burned and will start to crystalize from the heat sort of like glass which will block the proper flame rectification back to the control board. What i find really funny about flame sensors and thermocouples is that no one that I know of regularly practices sanding down thermocouples but will sand down flame sensors on a regular basis. Two different bi-metals in the thermocouple, not exactly the same as flame sensor but close enough.

[novice 39]

Thanks precise!

Sounds like the oxidation buildup and eventual no-op of the sensor is inevitable.

I can appreciate your stance, as a businessman, on replacing rather than cleaning the sensor, but I'm curious -- are the sensors ever really bad if the deposits can be removed, the insulator is not cracked, and electrical continuity is still there? Are they good as new after cleaning, or will they re-oxidate faster than a new part? Or does the activity of removal, cleaning, and reinstalling the sensor weaken/degrade it, loosen bonded connections, etc., causing it to permanently fail? (that would concern me if I was the technician.)

I'm not challenging you, I'm just wondering if next time mine gets dirty, I should insist the technician replaces it rather than cleaning it.

[s tek]

If your combustion air comes from a laundry room or close to one .Quit using dryer sheets softner. they will coat a flame rod in no time.

[precise temperatures]

I would think that it would weaken the sensor from its original state after you use steel wool on it. Not 100% sure on this but I am just using theory here. It makes sense to me that even more oxidation would occur once it is sanded due to more grooves in the rod to pick up more particles. That is my thoughts on it, but you should be ok by just sanding it down even though I wouldn't practice this unless it was 2:00 in the morning and my customer had no heat and I did not have a new sensor.

One good thing about it is that it is an easy fix and if it goes down again you know exactly what to do

[aaf2000]

The only flame sensors I clean are in older neighborhoods that still have old steel gas mains. The same furnace in newer subdivisions with plastic gas mains never quits because the flame sensor is dirty.

Conclusion: The culprit is dirty natural gas.

I have several LP furnaces in rural areas which flame sensors' never give me any problems.

I have not seen where laundry rooms make a difference on flame sensor callbacks. HSI's definately, but not flame sensors. The only commonality between all of my FS callbacks is old steel gas mains.

[kim]

I clean every flame sensor on furnace maintenence agreement. On a breakdown, I usually try to sell them a flame sensor. Its only $50 difference and less chance of callbacks.

I clean them with sandpaper. I figure if it is a solid rod why not do it the faster way.

Note: Talked to a rep about flame sensors. He said voltage to flame sensor is not reliable becuase you need a true RMS meter. But he said any microamp reading at all says the flame sensor is good and its a bad board.

[docholiday]

I've never seen a flame rod need replaced unless the procelin is cracked or the rod was burnt. Selling a replacement does not solve anything other than you have a new rod and a bigger bill.

[kim]

Its all about the warrenty.
If you try to sell them a new one and they opt for a cleaning, the next call is billable.

[beenthere]

Originally posted by docholiday
I've never seen a flame rod need replaced unless the procelin is cracked or the rod was burnt. Selling a replacement does not solve anything other than you have a new rod and a bigger bill.

You can bend the FS and it will still work, its just a piece of metal.

OK, you shouldn't bend them. :)

[docholiday]

You could probably rig a coat hanger to work. Yeah, dont bend them :)

[beenthere]

Originally posted by docholiday
You could probably rig a coat hanger to work. Yeah, dont bend them :)

I used a piece of brazing rod once.

Just to prove to a guy that there was nothing special about the rod itself.

[precise temperatures]

Originally posted by kim
Its all about the warrenty.
If you try to sell them a new one and they opt for a cleaning, the next call is billable.



Exactly!!

[mike3]

Use a jumper on a screwdriver in place of the flame rod..will work fine.. Just another troubleshooting trick,probably already used by many(or some)
Replacing undamaged flame rod is not something I would advise. Unless you need to bump up the bill for no reason

[Edited by mike3 on 02-07-2006 at 07:35 PM]

[tinknocker service tech]

Originally posted by mike3
Use a jumper on a screwdriver in place of the flame rod..will work fine.. Just another troubleshooting trick,probably already used by many(or some)
Replacing undamaged flame rod is not something I would advise. Unless you need to bump up the bill for no reason

[Edited by mike3 on 02-07-2006 at 07:35 PM]

never tried that. great idea
thanks

[mark beiser]

Heh, I have done the jumper on a screwdriver trick. Customer tried cleaning the flame sensor himself and managed to break the insulator. He then lost the sensor when he was running around looking for a place to sell him one.

I put a big wad of permagum on the end of my pocket screwdriver and stuck it down to the bottom of the burner compartment with the tip sticking up in front of a burner, then clipped a jumper wire between it and the control board. Worked like a champ for 3 days til I got back with the new sensor. :)

In my opinion, anyone that tries to sell a new flame sensor because the old one is dirty is ripping off thier customers. It only needs to be replaced if the insulator is broken or someone scratched it up bad enough that it gets dirty to fast. Sometimes you will run into a furnace that has recurring problems due to a design defect and the manufacturer will have an updated sensor design/location.

Never use sand paper to clean a flame sensor, for several reasons that have been gone over multiple times on this board.

[novice 39]

Thanks everyone. I believe next time the flame sensor is dirty, if the technician plans on cleaning it rather than replacing it, I'll ask him if he sands or uses steel wool. Maybe he can get it nice and shiny without a lot of scratches on it.

I probably do have dirty gas, but I can't do anything about that.

[precise temperatures]

i can't believe we are using pocket screwdrivers and permagum for a $XXX flame sensor????

Just change the part out.

>>>edit...

http://www.my-smileys.de/smileys2/033102sor_1_prv.gif (No pricing, due to site rules (http://www.hvac-talk.com/vbb/showthread.php?threadid=1241) )


[Edited by jultzya on 02-08-2006 at 12:24 AM]

[mike3]

Originally posted by precise temperatures
i can't believe we are using pocket screwdrivers and permagum for a $XXX flame sensor????

Just change the part out.

He did

put a big wad of permagum on the end of my pocket screwdriver and stuck it down to the bottom of the burner compartment with the tip sticking up in front of a burner, then clipped a jumper wire between it and the control board. Worked like a champ for 3 days til I got back with the new sensor.

>>>edit... please XXX pricing out of quotes. It only creates more work for the mod's when you don't. Thanks


[Edited by jultzya on 02-08-2006 at 12:27 AM]

[tinknocker service tech]

Originally posted by precise temperatures
i can't believe we are using pocket screwdrivers and permagum for a $XXX flame sensor????

Just change the part out.


i have not seen a flame senser this cheap
should not be posting inacurate costs in open forum

>>>edit... please XXX pricing out of quotes. It only creates more work for the mod's when you don't. Thanks


[Edited by jultzya on 02-08-2006 at 12:28 AM]

[mark beiser]

Originally posted by precise temperatures
i can't believe we are using pocket screwdrivers and permagum for a $XXX flame sensor????

Just change the part out.

>>>edit...

http://www.my-smileys.de/smileys2/033102sor_1_prv.gif (No pricing, due to site rules (http://www.hvac-talk.com/vbb/showthread.php?threadid=1241) )

I did, but on friday night, you gota do what you gota do to get some heat on for people until the parts house is open monday...

>>>edit... fixed post


[Edited by jultzya on 02-08-2006 at 03:01 AM]

[precise temperatures]

sorry about the post on the price. wasn't thinking and i was inaccurate with the price anyways.

[brainsurgeon]

1) Build up of material on a flame rod can be from the combustion air and gas byproducts . Sealed combustion can help if a) furnace is in laundryroom or moist basement dust ect.. 2) cleaning of the rod should be done on yearly inspections , use wire brush or dobby pad ,if using steel wool wipe off with lint free cloth , Note never use sand cloth or emery paper

[corny]

Originally posted by precise temperatures
Steel wool is correct to use, not sandpaper, but to be honest with you I have never offered this to a customer. I am in the repair business, not in the "temporary" repair business and to protect myself from callbacks that I cannot charge back to someone - either customer or manufacturer, I will not just clean it up and hope it works.

And to comment on what causes them to go bad, oxidation will form on them from the by-products of the fuel being burned and will start to crystalize from the heat sort of like glass which will block the proper flame rectification back to the control board. What i find really funny about flame sensors and thermocouples is that no one that I know of regularly practices sanding down thermocouples but will sand down flame sensors on a regular basis. Two different bi-metals in the thermocouple, not exactly the same as flame sensor but close enough.



There is nothing close about the workings of a flame sensor and thermocouple...the thermocouple has two conductors of different materials inside the shell which when heated generates a current...the flame sensor is merely a conductor that will withstand being immersed in a flame...a piece of copper wire would work for the flame sensor...if you could keep it from sagging...and keep it from contacting ground..except thru the flame.

You should be able to clean a flame sensor....just use something fine to polish the surface back after cleaning...00 steel wool seems to work fine.

[fixitguy]

Cleaning them, I used just a nylon scratch pad. Does a fine job.
Its fun to show the flashing FS light on RUUD/Rheem to the customer.

I usually try and get the customer to know the basic operation of their unit.:)