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Millivolt system testing when Pilot is on, but main burner not always lighting

Millivolt system testing when Pilot is on, but main burner not always lighting

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  #1  
Old 10-23-10, 06:09 PM
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Millivolt system testing when Pilot is on, but main burner not always lighting

I am trying to diagnose a problem with an old furnace. I have some pictures to help clarify what I have, a ThermoPILE system.

The problem is that the PILOT flame is on, but the main burner does not always light.

I cleaned all electrical contacts today with sandpaper, and made sure they were all tight.

I also made sure the PILOT line and BLEED line were not blocked. (Took them off and blew through them).

I also took out the THERMOPILE sensor, and cleaned it off with steel wool.











And this is a repeat , but I am trying to show that there is a steel connection(steel plate) between RED(Thermopile,pos) to TH1(thermostat,pos).

Also a steel connection(steel plate) between TH2(thermostat,neg) to L2(LIMIT switch, pos):


I was trying to use the "MILLIVOLT TROUBLESHOOTING CHART", on page 2 of this diagram:
http://www.robertshawtstats.com/spaw...oltSystems.pdf

But I'm not sure what connections to put my meter across.

For example, the chart says in TEST-A, to test across TP and TH for more than 100mV, with the thermostat contacts CLOSED. (On my gas valve, would that be RED to TH1, or RED to TH2, or something else?)

For example, the chart also says in TEST-B to test from TH/TP to TP for greater than 325mV, with the thermostat contacts OPEN. (On my gas valve, would that be TH1 to WHITE, or TH1 to RED, or something else?)

Also, when it says thermostat contacts CLOSED - does that mean with the thermostat temperature set to higher than the room temperature?

I attempted to do TEST-A, with thermostat set to turn furnace on(I assume that what what they meant by thermostat connections CLOSED?) and measured:
RED to TH2 = 123mV
WHITE to TH1 = 387mV
TH1 to TH2 = 20mV
RED to WHITE = 400mV
L1 to L2 = 26mV

For some reason I did not measure RED to TH1, or WHITE to TH2. Should I have?

Also, those readings were what actually displayed on my meter, when the dial was on the 2000mV range, and the 200mV range.

So I think I'm reporting the voltages correctly? That is, if the meter displayed 123 on either of the ranges(2000mV, or 200mV) - that means I measured 123 Millivolts?

If the gas valve is sticking, can this be disassembled and cleaned? Can it just be replaced?
 
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  #2  
Old 10-23-10, 06:50 PM
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I wouldn't touch that furnace with a 10 foot pole since it appears the gas to the pilot does not shut off with pilot outage. (Particularly important with LP.) Many houses have been blown to bits & people killed because of systems like that. If the furnace were otherwise safe, I'd replace the gas valve/pilot assembly. Sorry but that's the best advice I can give you on that system.
 
  #3  
Old 10-23-10, 08:57 PM
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The pilot burner is dirty and needs to be cleaned. You need to remove the nut that holds the pilot tuning into the pilot burner and remove and clean the pilot orifice as well.

The pilot burner isn't putting enough heat on the pilot generator to produce enough electricity to open the gas valve.
 
  #4  
Old 10-23-10, 09:42 PM
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Seattle,

I tried to clean the pilot opening. (Is that what you mean by pilot orifice)? This was a picture before I rubbed the opening with steel wool. Is that the correct way to clean it?

The pilot opening, and thermopile, look cleaner now - than in that picture.

When you wrote "You need to remove the nut that holds the pilot tuning into the pilot burner" - did you mean "turning" the pilot opening to face the thermopile sensor?
 
  #5  
Old 10-23-10, 09:51 PM
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Grady, I'd rather fix it. It has been in place for probably 15 years or more. What replacement part(s) would I buy? The newer valves I've seen have just 3 terminals, and this one has 6. How would the existing wires match up to a newer valve?
 
  #6  
Old 10-23-10, 10:30 PM
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Am I doing the voltage readings correctly?
 
  #7  
Old 10-24-10, 09:17 AM
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Yes, the pilot gas doesn't shut off. But by it's very nature, the main burner gas wont turn on unless the pilot is lit and generating enough electricity to open the main burner gas valve.

No pilot no main burner gas.

A more modern gas valve would have a separate thermocouple and would shut off both pilot pilot and main burner gas if a pilot outage occurred. But what's there is safe enough.
 
  #8  
Old 10-24-10, 09:20 AM
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Hi Seattle, Have you had a chance to read post #4, and #6? I am very interested in your answers.

thanks,
matt
 
  #9  
Old 10-24-10, 09:27 AM
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Originally Posted by mnalep View Post
Seattle,

I tried to clean the pilot opening. (Is that what you mean by pilot orifice)? This was a picture before I rubbed the opening with steel wool. Is that the correct way to clean it?

The pilot opening, and thermopile, look cleaner now - than in that picture.

When you wrote "You need to remove the nut that holds the pilot tuning into the pilot burner" - did you mean "turning" the pilot opening to face the thermopile sensor?


That should have been pilot tubing. There's a nut holding the pilot tubing into the bottom of the pilot burner. You need to loosen that, pull the pilot tubing off, remove the pilot orifice and clean it and the pilot burner.

Once you have the pilot orifice out you'll be able to clean the pilot burner out with a wire brush and by blowing out any debris and junk in it.

Reassemble it and you should be back in business.
 
  #10  
Old 10-24-10, 09:55 AM
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Seattle. OK thanks. Am I trying to clean rust, etc out of the pilot tubing? I did blow through it, but what is the proper way to clean the inside of pilot tubing?

So the pilot opening is facing the right direction? That is,the pilot flame is not supposed to point directly at the thermopile generator? Instead the pilot flame points forward, and is on the left of the thermopile generator?

Also, any input on how to test the gas valve terminals with mulitmeter. I was trying to do TEST-A and TEST-B in that linked document, but I have 6 screws versus the article describing 3 screw terminals.
 
  #11  
Old 10-24-10, 11:40 AM
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You can blow through it if you wish, but I've never seen debris collect in pilot tubing.
 
  #12  
Old 10-24-10, 11:43 AM
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Oops, I think I misunderstood your earlier directions.
 
  #13  
Old 10-24-10, 12:26 PM
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I forgot to mention that I got the main burner to light on 2 occassions by tapping on either the gas pipe before the main shutoff valve, or on the honeywell gas millivolt valve itself.

Does that indicate more a gas valve problem or a thermopile generator/pilot flame problem?
 
  #14  
Old 10-24-10, 12:57 PM
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In your picture number 3, that shows gas valve wiring......and the fact you ask in your opening post about how to test when it says TH/TP(and your gas valve does not specifically have written on it TH/TP the way some gas valves do.......the fact that you illustrate that you have a metal plate bridging TH with TP, means that is your "common". That those two terminals, bridged together as a unit are your TH/TP, which is your "common". That means for millivolt testing per the testing instructions in your OP, you test from either the lone TH or the lone TP , over to the bridged(metal plate) TP/TH to get your measurement.
 
  #15  
Old 10-24-10, 04:25 PM
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So what you are calling the "lone TH" is "TH1" on my valve?

And what you are calling the "lone TP" is "RED" on my valve?

I'm not following what you mean by "over to the bridged(metal plate) TP/TH" means what? (do you my "WHITE", "RED", or "TH1" or ?)

Which 2 pair of terminals do I use for TEST-A?

ANd "TEST-B", etc.
 
  #16  
Old 10-24-10, 04:36 PM
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I searched for that gas valve, and found this one as the replacement:

http://americanhvacparts.com/Merchan...tegory_Code=GV

How would I convert the 6 wires I have now, to that (looks like 3 terminals) gas valve?
 
  #17  
Old 10-24-10, 05:48 PM
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some reason I did not measure RED to TH1, or WHITE to TH2. Should I have?

Yes, I believe those 2 terminals are the "operator" terminals. The reading there will tell us how much voltage is going to the operator. The operator opens the valve.
Is there any yellow in the pilot flame? As mentioned by S/P, the pilot may need cleaning. The generator portion of the pilot is where the voltage comes from to operate the system and if the pilot is weak, the valve won't open or slow to open.
 
  #18  
Old 10-24-10, 07:52 PM
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DON'T replace the gas valve. Clean the pilot burner and pilot orifice. It's obvious from the pictures that these are past due for cleaning and a dirty pilot is the most common reason that the gas valve wont turn on.

By contrast, the gas valve operator tends to be very reliable and it's rare that control valve needs to be replaced.
 
  #19  
Old 10-25-10, 12:33 PM
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mbk3, There was some yellow in the flame. A little less after being cleaned. Is yellow bad? there is a lot of blue at the base.
 
  #20  
Old 10-25-10, 03:31 PM
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Seattle, It has come on a couple of times. I'll keep an eye on this and perhaps clean the pilot orifice better if the main burner starts failing to ignite again. Either way, I'll post back soon.
 
  #21  
Old 10-25-10, 05:46 PM
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Yes yellow typically means a linted primary air opening in the pilot burner or and oversized orifice. I vote on lint. I noticed you have a PG-9 pilot generator. This probably the most common PG in years. Please notice the bright shinny plate with one screw in the middle on the pilot. Remove the screw and then remove the plate. You will see a hole in the pilot burner. Take a straw or small rubber hose and blow thru the hole. If you really want to do it right remove the pilot and take the orifice out and than blow thru the opening. Make sure not lint ,bugs, or spider nest inside.
 
  #22  
Old 10-25-10, 05:50 PM
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mbk3---



You are obviously a master pilot burner cleaner!


From the picture it's obvious to me that pilot burner needs cleaning badly.
 
  #23  
Old 10-25-10, 06:05 PM
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S/P I couldn't see the flame in the picture. But, as you know, working for a utility you clean thousands and I do mean thousands of pilots in your career
 
  #24  
Old 10-25-10, 08:51 PM
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I know I hopefully getting ahead of myself, but I like to know what I could do if I had to with that gas valve...

First, is there any way to take apart a gas valve and recondition, or clean it - that is, if turns out to be sticking?

Second, I found this gas valve listed as a replacement - Millivolt Gas Valve 1/2" Gas Pipe Inlet 3/4" Outlet (Honeywell): American HVAC Parts - but it looks like maybe it only has 3 terminal screws. (versus mine that has 6 terminals).
 
  #25  
Old 10-26-10, 08:29 AM
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NO you cannot field service this valve. And yes you are getting ahead of yourself.
three terminals presents no problem if we get to that

Please do as directed with the pilot first.
 
  #26  
Old 10-26-10, 08:47 AM
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mbk3, OK. I'll follow the playbook, and thanks for helping.
 
  #27  
Old 10-26-10, 09:00 AM
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Don't make S/P and me get on a plane and come back there and slap you around.

You'll get it going. Good luck. (although luck should have no part in this business)
 
  #28  
Old 10-26-10, 09:04 AM
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One more thing. What brand is it? First I thought it was a Holly and then I thought a Sears brand.
 
  #29  
Old 10-26-10, 06:34 PM
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The valve is a Honeywell.
 
  #30  
Old 10-26-10, 07:15 PM
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He got the advice to clean the pilot burner on the second post. 23 additional posts and he still hasn't done the job.

I've wasted enough of my time screwing around with this. If he wants to change out the gas valve, let him figure it out.
 
  #31  
Old 10-26-10, 07:54 PM
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Not the valve ...the furnace name
Sorry I should have said furnace
 
  #32  
Old 10-26-10, 08:50 PM
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Seattle,

I have cleaned the pilot. I've made references to that. I am just worried if I find out a week, or month from now, that I have a valve problem - I want to be ready to change that very quickly if I have to. So I'm just doing the research now, instead of in December. Sorry, about any confusion.
 
  #33  
Old 10-26-10, 08:54 PM
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mbk, It's a Luxaire furnace...
 
  #34  
Old 10-27-10, 05:07 PM
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So, in case I need a new valve, I've taken a picture of the schematic for my current gas valve, and found the manual for the new replacement gas valve I'd use, from White-Rodgers.

Below is the schematic for my gas valve:


Below is the replacement valve from White-Rodgers, with the schematic for it on PAGE, FIGURE-3:
http://www.emersonclimate.com/en-US/.../0037-6264.pdf

I think I see how the 6 wires from my old one would map to the 3 terminals, and 1 wire ("power unit") on this one.

I would need to make sure I get the correct input pipe size as the
36C03(U)-333 is 1/2"input and 3/4" output, while the 36c03(U)-433 is 3/4" input and 3/4" output.

I'd have to re-rout the pilot line from the pilot valve, and cap the pilot valve outlet. Also have to remove the regulator and put in a longer piece of black pipe. Then attach new valve, and wires.

The only thing I do not see in the new valve diagram is that bleed tube?

Does this all sound right?
 
  #35  
Old 10-29-10, 02:43 PM
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Have you completed the task outlined in post #21??

Lets talk about the valve replacement later. If you have completed #21, now we need some reads.
 
  #36  
Old 10-30-10, 07:28 AM
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mbk3, yes, and so far the furnace seems to be working. I blew through he plot tube after disconnecting it from the pilot valve. I also hit the pilot cover with steel wool and sandpaper to clean the whitish crud off it. Also cleaned the pilot generator with steel wool.

I just have a fear it is going to quit on me later, so I was trying to get all 'my ducks lined up ahead of time' - as the saying goes.

I think what makes me uneasy is that the first I got the main burner to light was after i tapped on the pipes with a cresent wrench.

But, If I'm lucky - I won't have to do anything else.

In either case, you and Seattle have been most helpful, and I sincerely thank you for your help.

I will post in a few days or so how the furnace is working.
 
  #37  
Old 10-30-10, 10:19 AM
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He'll be Baaaack!

Judging from your last post, you still haven't done the job right.


You say you disconnected the pilot tubing at the pilot valve and blew through it. That is an ineffective way to clean a pilot burner, and will very likely result in a return of the symptoms before long.

You need to clean the pilot burner and pilot orifice. You need to remove the pilot burner and pilot generator, then remove the brass nut holding the pilot tubing in place and remove and clean the pilot orifice, then clean the junk out of the pilot burner, Mbk3 gave good directions on cleaning the pilot burner.

But no. You want to follow your own eclectic notions. You can do that without wasting our time asking for advice you ignore.
 
  #38  
Old 10-30-10, 05:59 PM
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I figured that by disconnecting the Pilot tube at the pilot valve, and blowing through that tube, I was in effect doing the same thing as mbk3 suggested "Take a straw or small rubber hose and blow thru the hole." I thought the pilot line was same thing as putting a straw or rubber hose on the orifice hole and blowing.

But he did also say "If you really want to do it right remove the pilot and take the orifice out and than blow thru the opening", which I have not done.

I will take it apart and remove the orifice. (I just realized that the orifice was a separate piece in the pilot burner - not just the opening in the top of the burner).

You know I'm not trying to get anybody angry, and it seems like I have. I am sorry for that.
 
  #39  
Old 10-30-10, 10:09 PM
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Read MBK3s post #21 carefully. This gives directions for additional disassembly and cleaning of the pilot burner needed to do a quality job in addition to cleaning the pilot orifice.
 
  #40  
Old 11-09-10, 11:37 AM
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Sorry it took me so long to get back here. I've had some other problems that needed attention.

So I took apart the pilot burner and orifice, and cleaned it out.

I took a couple of still pictures of the flame before and after. And a video clip of the flame is posted below also.

I also bought a new limit switch and installed it, as the old one was looking kind of rusty. You can see the two limit controls side by side below.

The furnace has still been working well, although we have had temps in the 60's this last week. So it's been a light duty test.

The pilot generator was putting out about 750mV on my last meter reading. I was worried at first because my initial reading was around 600mV. I took it all apart and made sure it was real clean, and after I put it back in the 2nd tome the reading was at the normal 750mV. Not sure why it was low the first time?

So I am hoping this furnace is set.

Thank you guys for helping me with this!!!



http://img121.imageshack.us/img121/3128/img0253vh.jpg


http://img607.imageshack.us/img607/7226/img0266b.jpg


http://img202.imageshack.us/img202/5348/img0267zf.jpg


http://img829.imageshack.us/img829/2461/img0283ed.jpg


http://img560.imageshack.us/img560/9652/img0290q.jpg


http://img201.imageshack.us/img201/5387/img0292i.jpg


http://img577.imageshack.us/img577/3131/img0295h.jpg


http://img152.imageshack.us/img152/2363/mvi0254.mp4

http://img152.imageshack.us/img152/2363/mvi0254.mp4
 
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