Old Wall Gas Furance - won't light, need basic info

[jdf405]

Hi,  I've got an older natural gas wall furnace in my house.  The pilot light won't stay lit.   It goes out right away after I release the knob, even if I hold it down for several minutes.  I believe it is the pilot sensor or something like that. 

Something funny was done to this heater before I owned the house.  Someone inserted a red pushbutton switch into the line that connects the thermostat to the heater.  The switch has a semi-rigid tube coming out of it and it goes to near the pilot light.  It doesn't seem to have any effect.

I am very handy but I know nothing about thermocouples, pilot lites etc...  Can you give me a basic primer on how/where to start trouble shooting my problems?  I can take some digital pictures and post them for you if that would help.

Thanks and Happy Holidays!

Jonathan

[AccApp]

First thing to try is replacing the thermocouple. It is the metal bit washed by the flame and it has a tube(copper?) which goes back to the gas valve and screws into the gas valve. They fail on a fairly regular basis and they cannot be tested by most readily available meters. You can get thermocouples at my Home Depot. Take the old one out and bring it with you. If the local home depot can't help you, try a plumbing supply store. Post a pic if you can.

[Budget Appliance Repair]

[user=15048]jdf405[/user] wrote:

Something funny was done to this heater before I owned the house. Someone inserted a red pushbutton switch into the line that connects the thermostat to the heater. The switch has a semi-rigid tube coming out of it and it goes to near the pilot light. It doesn't seem to have any effect.

Does the red pushbutton snap/click when you push it?? It sounds like this maybe a pizo electric ignitor, (the type you see on bbq's), that someone may have rigged up to this older heater so as not to have to use matches to light the pilot. Try pushing the button when holding the gas valve knob in, (for lighting the pilot), and see if the pilot lights up.

The most likely problem for the pilot to not stay lit is a bad thermocouple -- best deal would be just to replace the thermocouple and give it a try, a new thermocouple shouldn't cost much more than $5.00.

[dkpd1581]

The red push button switch with electrical wiring to it may be some type of roll out or over temperature switch.  The fact that it is tied into the t-stat wires leads me to believe that it is a safety switch. 

When the switch senses flame in the wrong area or two much heat, the switch opens and cuts 24 volts to the system thereby shutting the heat system down.  That it has the push button is typical for such a switch - called a "manual reset".

The purpose behind the manual reset is that the condition sensed is considered serious and requires human intervention.  Some switches are automatic reset and require no attention.  That your's is possibly manual reset and that by pushing the button resulted in no change would mean that no serious condition has occured.

[jdf405]

Hi All, thanks for all the info.  Here are four pictures.  In this first one you can see this switch thing in the lower right corner.  The switch itself has been jumpered out of the circuit.  The thermocouple that comes out of it does nothing aparently.

In the mean time I realized this heater actually has 3 (yes THREE) pilot lights. I lit the other one on the backside and now it stays lit and will heat the house.

Next post has next pic...

[jdf405]

Here is photo 2. - A shot of the inside cover of the switch.  Funny thing is - Gardena, CA is right down the road from where I live...

[jdf405]

Here is photo 3.  This is the "2nd" pilot light I lit.  This one did heat its thermocouple and keep the gas on after I let go of the knob.

What is all that white stuff?  Do I need to clean this thing out?

[jdf405]

Photo 4 - taken below photo 3.  This is the back of the main control thing (that has the on/off, pilot knob on it).  It has a thermocouple wire that connects to the pilot that actually does something. 

Is there a way to adjust the pilot light size?  They seem rather large (almost 1.5") and uses a lot of gas).

THanks!

[hvacdrd]

Does it need cleaning - ya think? The white stuff is ash from all the dust that has been burned over all the years. I would recommend pulling the burners, blasting the inside of the heat exchager with compressed air (be prepared for a dust storm.)

As for the pilot/wiring configuration, what a mess. Looks like they are using the red button switch (baso control) as a second pilot safety, the gas valve has the same type of safety built-in. Usually there is only multiple pilots when the burner is large or very long. On a wall furnace I can't imagine why???

Your pictures also reveals the use of a known hazardous flex connector. See the green corrosion near the flare fittings? Replace the connector unless your homeowners insurance is up to date.

Any reason why there is two connectors? Where does the second one go? I can't make it out in the photo.

As for 3 pilots, do you mean 3 flames from one pilot burner? That would be more like it - where are the other 2?  As far as adjusting, start by disassembling and cleaning the burner & orfice. Most gas valves have and adjustment screw to adjust the flame size. Make sure the top 1/4-1/2" of the thermocouple is engulfed in the pilot flame.

The control made in Gardena CA shows it's age. Nothing has been made in the USA for a pretty long time. Where does the thermocouple from that pilot switch go?

[applianceman18007260692]

thats a millivolt heater .if you had a millivolt meter you could check the output on it . the pilot chances are you need to change the thermopile generator thats the pilot light assy , its a fat thermocouple

[Guest ahammer48]

Hello

Give a  applman18 a cigar. Most wall heater use a thermopile (millivolt generator). Because most don't use any electricity the thermopile actually generates electricity when put in a pilot flame and that electricity(millivolt) is what is used to open the gas valve. Most had the thermostat mounted directly on the heater.

But it sounds like Ur heater is connected to a wall thermostat? If thats true then there maybe a 24vac transformer involved here and that could B the reason for the box with the red push button.

Looking at the pictures I don't C the thermopile at the pilot assembly.

Do U have 1 or 2 pilot assemblies?

The box with the red push button looks like it has a copper tube coming off of it. I haven't look up the part number yet but agree that it's a safety device that also needs to sense a pilot flame and has a thermocouple (just senses flame but doesn't generate electricity). When immersed in a flame U should be able to push that button and it should stay latched and not pop back up again.

Yes, Ur heater should be cleaned out.

Hope this helps:)

[Budget Appliance Repair]

Only thing is, that thermocouple/safety (red push button) has been bypassed as Jonathon mentioned, (notice that little wire between the two terminals?).

It almost looks like, (from that conglumeration of fittings and flex tube), that someone may have made a double wall heater out of two single wall heaters. Unless maybe this was an original real old double wall heater and it actually used two pilots, one for each side of burners instead of like the new modern ones which only have one pilot assembly positioned between the two burners or the two burners have ignition crossover ports.

If the thermocouple that feeds that safety device was bad or the flame it was positioned in where to go out it would just open the t-stat line, (just like turning the t-stat off). The way it is now it is bypassed and has no function.

[Guest ahammer48]

Hello

Good catch.

Didn't C that jumper wire.

>>>>>>jd405>> From the pictures I would REALLY recommend U replace that unit. Its unsafe!!  Even if your not gonna stay in the home that much longer, a new heater makes a great selling point.

Hope this helps:)