HEIL DC90 intermittently fails to heat

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  #41  
Old 04-04-08, 08:46 PM
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Originally Posted by pflor View Post
I'm not sure I know what "puddy" is. Do you perhaps mean "putty"?
Yes... I did mean putty. Sorry, I've only been speaking English for 38 years or so.

are you maybe referring to the ceramic cover that surrounds the flame rod an isolates it from its holding bracket?
The wires that come from the bracket go through the wall of the combustion chamber and on to the smartvalve.

Where the wires penetrate the wall, it is "sealed" with what looks to be plumber's putty... or at least a fair approximation of it. It is still pliable, but I wouldn't be surprised if it wasn't a perfect seal.

I'd love to know what happens with the micro-amp reading when the main burners fail to ignite. I think that's the ultimate clue needed to solve this mystery.
I suppose I could try setting that up tomorrow morning/afternoon. That probably would be instructive.

You won't break anything by putting a bit more force than usual in loosening the cap-screw that would allow you access to the inner screw for pilot-gas pressure adjustment
Actually, I got the cap-screw off (and I did think I had broken it). It was the inner screw that seemed too tight to move.... so, I didn't at the time.

No sealants of any kind on the threads of the pilot burner and couplings when accessing the orifice. The connections there are strictly "pressure" fit...a small adjustable wrench is all that is needed there.
OK... I'll give that a look. I have a leaking water softener (what next?) that may end up taking priority, but we shall see.
 
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  #42  
Old 04-05-08, 10:41 AM
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Random thought...

Could it be the thermostat in some way? Whenever I jumper W-R, the furnace goes to full ignition.
 
  #43  
Old 04-05-08, 11:57 AM
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Very unlikely that the t-stat is the problem.

The t-stat is just a "nice looking" switch, it does the same job as the jumper you've been placing between R & W at the furnace's terminal board, except that it does so automatically, based on the temperature it senses in the surroundings.

If the t-stat was the problem then on a call for heat, the inducer blower won't kick ON, nor the ignitor would glow, nor the pilot light-up.

t-stat puts the jumper in place and that is the end of its share of work. The ST9120C notices and takes action...it's time to work. The board checks that things are safe (safeties not tripped), turns inducer ON and pressure switch instructs the smart valve to get going. Smart valve goes into ignition duty and once the presence of the pilot flame is confirmed (the micro-amp signal), smart valve allows gas to main burners and heating process starts.

And it is in this last step that you're having the problem. The pilot is lit but the main burners won't (randomnly)

so... there's something fishy with the pilot flame, or the integrity of the flame-rod, or the ground electrode pathway, or the smart valve itself (erratic performance). A pic would help. The path to ground is via the pilot-burner gas tube...so it'd better be tight, not loose. And I wonder if your board has a ground connection that I do not know of but may be loose or rusted (you had indicated no ground connection exists at the board).
 
  #44  
Old 04-06-08, 05:00 AM
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I didn't say that all of my random thoughts were good thoughts (you should have seen what I originally wrote then wisely edited a few minutes later)

The meter I am using (Fluke 189 series) has a logging feature, so I have had it hooked up several times over the weekend to see if we can catch the reading at pilot-only times.

Of course, the furnace has gone to full ignition every time.

... and I haven't had time to clean the pilot orifice yet. I hope to do that today.

The one interesting thing that I noticed while trying to take micro-amp readings on the flame rod (both with leads I held there and with clips during the unattended logging) was that the meter would display "Leads" on the display briefly and intermittently. The manual indicates that it might be a fuse issue, but isn't very helpful beyond that.... nor can I find anything on-line. So, I am just wondering if that is indicating some sort of continuity with the flame sensor after all.

Which brings me to another thought... how do we know that the smart valve is correctly interpreting the reading from the flame rod?

How does one ensure the pilot-burner gas tube path to ground?

I am assuming a grounding connection from the board would/should be a (green) wire off to somewhere?
 
  #45  
Old 04-06-08, 05:42 AM
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Originally Posted by s2zeller View Post
The meter I am using is a Fluke 189 series
Good meter!

Originally Posted by s2zeller View Post
The one interesting thing that I noticed while trying to take micro-amp readings on the flame rod (both with leads I held there and with clips during the unattended logging) was that the meter would display "Leads" on the display briefly and intermittently. The manual indicates that it might be a fuse issue, but isn't very helpful beyond that.... nor can I find anything on-line. So, I am just wondering if that is indicating some sort of continuity with the flame sensor after all.
Here I wouldn't know what to tell you even if my life depended on it

Originally Posted by s2zeller View Post
Which brings me to another thought... how do we know that the smart valve is correctly interpreting the reading from the flame rod?
If the micro-amp readings never fall below the 1.3 microamps (in other words, if they stay normal at all times), then the smart valve is "randomnly malfunctioning and should be replaced. But if it came to that, and I was in your shoes, I would not only replace the smart valve but the pilot/igniter/rod assembly as well (they may even come altogether in a box)

Originally Posted by s2zeller View Post
How does one ensure the pilot-burner gas tube path to ground?
by making sure that (a) the pilot tubing connections are firm (and rust free) from the pilot burner to the gas valve, and (b) by making sure the connection to ground from the board is sound as well...but here is where a pic could help, since you report not seeing such connection, and indeed, some of these boards don't have one other than the screws that mount them on their bases. [/quote]

Originally Posted by s2zeller View Post
I am assuming a grounding connection from the board would/should be a (green) wire off to somewhere?
very good assumption, though not always the case.
 
  #46  
Old 04-06-08, 09:49 AM
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"Leads" on screen display? I'll take an uneducated guess; it's telling you something wrong with the leads. Either bad connection with them, or you have them reversed (for like DC testing you have to have the polarity right), or you have chosen the wrong 2 of the 3 holes in the meter to plug your red and black lead wires into for that particular test? Just taking a stab at it.
 
  #47  
Old 04-06-08, 10:00 AM
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Originally Posted by ecman51` View Post
"Leads" on screen display? I'll take an uneducated guess; it's telling you something wrong with the leads. Either bad connection with them, or you have them reversed (for like DC testing you have to have the polarity right), or you have chosen the wrong 2 of the 3 holes in the meter to plug your red and black lead wires into for that particular test? Just taking a stab at it.
The "bad" connection is what I am thinking as 99.9% of the time the meter is reading (what appears to be) correctly... and I have the manual in front of me (with pictures even ) to confirm lead wire placement.

Tho' to be absolutely clear, I am supposed to be measuring microamps DC, correct?

I did the meter self-diagnostic on the fuses, and those check out.

So, I am just wondering if this *could* indicate that the flame rod is intermittently failing... sometimes longer than others.

As I mentioned, the furnace hasn't failed in the last couple of days. Other than having the meter hooked up, it has also been warmer so it hasn't gone on as much either (in fact, it didn't fire at all last night). We are supposed to return to cooler days/evenings by mid-week, so I'm hoping that I'll be able to catch the pilot-only problem with the meter.
 
  #48  
Old 04-06-08, 10:09 AM
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I prefer to not get TOOOO involved with this thread, as pflor has worked so hard on this, and it is very time consuming, and I am jumping all over this board on so many threads that I can only handle so much. There are regular furnace guys here who make their living at this (I'm a jack of all trades guy), that should be able to help out, also.) But I wanted to share a couple things that may help steer the thread to a possible solve after quickly reviewing some of the stuff said.
 
  #49  
Old 04-06-08, 01:16 PM
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Originally Posted by ecman51` View Post
I prefer to not get TOOOO involved with this thread, as pflor has worked so hard on this
Ecman: the more, the merrier... I sure do not claim ownership of a thread. just here to help when possible
 
  #50  
Old 04-06-08, 01:39 PM
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Originally Posted by s2zeller View Post
Tho' to be absolutely clear, I am supposed to be measuring microamps DC, correct?
Correct! and the exact term to describe the type of electrical signal that is being generated, is: rectified DC current
 
  #51  
Old 04-06-08, 07:02 PM
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Well, the orifice appeared clean... very shiny, no carbon or metal flakes and a nice hole down the middle.

I was, however, surprised to see a dull layer of carbon on the flame rod as I'd cleaned that a month or six weeks back and thought I would have noticed the dullness. So, a bit of Scotch-Brite and a minute later and it was all back to being shiny and smooth.

Could it have gotten that carbon layer again so quickly, or did I just do a poor job the first time around?

I also measured the resistance in the pilot tube (from the locking nut at the pilot assembly to the locking nut at the SmartValve) and got something in the neighborhood of 1 Ohm.

The only other thing of note was a faint whiff of gas when I turned the gas supply back on after re-assembling everything. It was clearly coming from the SmartValve. I'd smelled a slight trace before, so I assume that this is normal?
 
  #52  
Old 04-06-08, 07:09 PM
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I think you may just have found out the reason for all the grief your furnace has been giving you, namely "the soot build-up" on your flame-rod.

Yes, they do soot-up rather quickly, 6 months to a year. And if the pilot flame is a bit on the weak side, it is also sootier...perhaps your pilot burner gas pressure needs some strengthening after all. The stronger the flame, the more air it will induce and the more bluish (and less sootier/yellowier) it will be.

And the trace smell of gas you noticed is quite normal.

resistance measurement is also O.K.

The good news (you see, there's a silver lining to everything in life) is that after all this work, by now there is nothing about your furnace that you do not already know.
 

Last edited by pflor; 04-06-08 at 07:37 PM.
  #53  
Old 04-07-08, 05:03 AM
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Now for the interesting observation...

After going to bed, I realized (OK, it was strongly suggested to me ) that I hadn't actually confirmed that the pilot would come on and stay on.

So, I turned the thermostat up and went to the basement, looked in the porthole, and... it was only pilot.

And...

The pilot was mostly orange now.

I powered the system down, and restarted it.

This time the pilot was mostly blue - but there was orange in there that I don't recall being in there before - and the furnace went to full ignition.

It also fired up nicely this morning, tho' again the pilot is looking a little more orange than before.

Since we had not had the furnace service for a couple of years (at least), I'm still wondering if something else is going on....
 
  #54  
Old 04-07-08, 05:45 AM
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Probably nothing unusual there. Just make sure that the threaded connections at the valve and pilot are nice and tight.

Orange flame? you may need to increase the pilot burner line pressure by a tad. A slightly higher pressure will do it.
 
  #55  
Old 04-07-08, 05:55 PM
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The furnace again failed to go from pilot to full ignition this afternoon. The thermostat was turned off and left that way for a few hours, so I hooked up the meter to the flame sensor when I got home and turned on the thermostat.

And it stayed at pilot!

The readings bounced around a lot (between 3.2 and 4.1) with the following characteristics:

- for periods of a couple of seconds it would "settle" in the 3.55 to 3.8 range... these stable periods would be approximately 20% of the time

- the rest of the time, it bounced around several times a second

- it only went over 4.0 maybe one out of every twenty readings (so once every 4-5 seconds and then only for a few tenths of a second at best).

I tried to adjust the pilot (which seems back to its blue self this evening) but found a couple of things confusing (big surprise, I know ).

The documentation says:

1) Controls are provided with adjustment screws
set at the maximum pilot flow position.

and

2) Turn the inner adjustment screw clockwise to
decrease or counterclockwise to increase the pilot
flame.

So, I find that I cannot turn it clockwise at all.

I *can* turn it counterclockwise, but this does not yield a larger pilot that I can tell.

Also, if I go too far counterclockwise, I start smelling more gas and the adjustment screw gets very loose.

So, I put it back the way I found it (i.e. so it can't go clockwise any farther).

The one thing I did notice with the pilot that - while it is now pretty much completely blue - it is not symmetrical. That is, it "leans" away from the flame sensor (this is when it is by itself or surrounded by fully-ignited flame jets).

Could there be some sort of draft or misalignment of gas supply relative to the flame rod/igniter?

Am I pretty much at the stage of getting a new flame rod/igniter assembly?
 

Last edited by s2zeller; 04-07-08 at 07:18 PM.
  #56  
Old 04-08-08, 04:11 AM
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Fluctuating micro-amps is no reason for concern, so long the reading does not go below the minimum Honeywell indicates (1.3 I believe).

When it comes to tests, all that could possibly be tried has been done by you with regard to your furnace. In your place I would buy a new smart valve & ignition set (igniter+electrode set) and replace first the ignition set to see if it fixes the malfunction...then proceed with the gas valve replacement if it does not. Smart valves do go bad.

The unplugging and re-plugging of wire harnesses, if not done gently, may also have a negative effect on the soundness of the electrical continuitiy of them (though I don't think that's a reason for concern in your case). Hopefully a new smart valve comes with new wire harnesses. If so, consider replacing them too.
 
  #57  
Old 04-08-08, 04:24 AM
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Originally Posted by pflor View Post
Fluctuating micro-amps is no reason for concern, so long the reading does not go below the minimum Honeywell indicates (1.3 I believe).
Nope, never went below 3.2 when I was watching it... just never got above 4 for more than a tenth of a second or so.

I'm leaning toward getting (if available) the whole pilot assembly (flame rod, igniter, ground electrod, bracket, pilot outlet) as the pilot outlet (not sure what the proper name is... the bent metal where the pilot flame originates from) is very corroded anyhow.

I appreciate your taking the time to get me through this. While I was leaning toward the replacements you've suggested initially, it is nice to have done the work to confirm that they really are good candidates for the problem.
 
  #58  
Old 10-18-08, 07:46 AM
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After an unfortuante stretch of warm weather in which we didn't use the furnace, I finally got around to installing a new igniter/flame sensor.

And...

The furnace failed to start the first time.

However, since then, it has actually started about 80% of the time... which is better than it was doing in April.

So, I'm thinking that that was at least part of the problem.

I expect to have a new valve installed by mid-week, so I'll post back on what happens afterward.
 
  #59  
Old 10-26-08, 05:10 AM
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After a couple of days with a new SmartValve installed, the furnace has not missed an ignition.

So, once again, thanks pflor for your painstaking effort to arrive at the proper solution. I hope your customers appreciate your approach!
 
  #60  
Old 03-13-13, 02:44 PM
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Currently having the same exact issue with our Heil DC90

I realize that your original post on this was 5 years ago, but just wondered if replacing the smart valve on your furnace permanently fixed the problem? We've already had a technician replace the heat exchanger which did nothing.
 
  #61  
Old 03-13-13, 05:58 PM
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Welcome to the forums.

The original poster has not been active for about three years so I doubt you will hear from him.

Hopefully one of the pros will be along soon. I am curious as to why the tech would replace the heat exchanger to resolve an ignition problem.
 
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