Payne 394JAW pilot problem


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Old 11-17-09, 05:23 PM
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Payne 394JAW pilot problem

I have a Payne 394JAW03645 furnace. When the thermostat triggers, the ignitor fires and the pilot lights as it's supposed to. The ignitor stops firing and about 10 seconds later the pilot goes out (you can hear the gas shut off). This furnace has a 3 wire pilot burner so I thought something had went wrong with the bi-metal switch in there which senses the pilot is lit. So I replaced this at $100. This did not solve the issue. The issue remains with the new pilot burner. Any ideas on things to check?
 
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Old 11-17-09, 06:53 PM
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Here's the wiring diagram

 
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Old 11-17-09, 07:11 PM
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I checked the voltage between gas 1 and gas3 and before thermostat kicks it's about 4v...then the ignitor fires and pilot lights and it goes to 15-16v.
 
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Old 11-17-09, 08:00 PM
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So. The pilot burner lights.

I'm supposing it stays lit and the spark keeps operating for about 20-30 seconds or so.

Then the spark shuts off.

Ten seconds or so later the pilot burner shuts off without the main burner lighting.

Then it goes back to the first step above, relighting the pilot and repeating this cycle over and over again.

Is that right?

If so, you probably have a burned out hold coil. Pull the wire off terminal 4 of the gas valve and test for continuity between gas valve terminals 3 and 4. If it's an open circuit, the gas valve needs to be replaced.


If my inference at what is happening is wrong, you need to correct me.
 
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Old 11-17-09, 08:13 PM
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Originally Posted by SeattlePioneer
So. The pilot burner lights.

I'm supposing it stays lit and the spark keeps operating for about 20-30 seconds or so.

Then the spark shuts off.

Ten seconds or so later the pilot burner shuts off without the main burner lighting.

Then it goes back to the first step above, relighting the pilot and repeating this cycle over and over again.

Is that right?

If so, you probably have a burned out hold coil. Pull the wire off terminal 4 of the gas valve and test for continuity between gas valve terminals 3 and 4. If it's an open circuit, the gas valve needs to be replaced.


If my inference at what is happening is wrong, you need to correct me.

Yes your understanding of what happening is correct, except it doesn't seem to automatically keep repeating the lighting procedure (if you mean immediately after it goes out) If I shut the thermostat off and redo it it repeats what you've noted. I pulled the wire off 4 of the valve and tested between 3 and 4. Continuity was good.
 
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Old 11-17-09, 08:17 PM
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Sorry. I pulled the 3 wire off and tested. That showed continuity between 3 and 4.

I replaced the 3 and pulled the 4 wire. Tested between 3 and 4 and there was no continuity, so I take it my gas valve is hosed.

If so any ideas on the replacement? It looks like it says 646AX...hard to read as it's worn, but I think it says that.
 
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Old 11-17-09, 08:39 PM
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Is the valve more or less cubical? That was the original valve, which tended to fail within a few years.

The replacement valve is kind of a flat rectangular solid, often with a blue control valve.
 
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Old 11-17-09, 08:44 PM
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Originally Posted by SeattlePioneer
Is the valve more or less cubical? That was the original valve, which tended to fail within a few years.

The replacement valve is kind of a flat rectangular solid, often with a blue control valve.
Here's a pic of it.
 
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Old 11-17-09, 08:45 PM
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Originally Posted by rrwantr
Yes your understanding of what happening is correct, except it doesn't seem to automatically keep repeating the lighting procedure (if you mean immediately after it goes out) If I shut the thermostat off and redo it it repeats what you've noted. I pulled the wire off 4 of the valve and tested between 3 and 4. Continuity was good.

If it's not repeatedly cycling as I described, it may be something different.

If it's not cycling, then I'm supposing:

The pilot lights.

The spark ignitor keeps sparking, often at a reduced rate once the pilot lights.

After 20-30 seconds or so the spark shuts off altogether.

Then the pilot burners shuts off and stays off until the thermostat is turned down and then up again.

Is that right? If not, please correct any discrepancy.
 
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Old 11-17-09, 08:49 PM
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Wow! I see you have the original valve manufactured in 1987! Usually those would have burned out LONG ago.

The replacement valves virtually never fail.


You may want to take pictures of a couple of the burners after you've brushed them off. Sometimes the burner ports can rust out and the burners would need to be replaced.
 
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Old 11-17-09, 08:50 PM
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Originally Posted by SeattlePioneer
If it's not repeatedly cycling as I described, it may be something different.

If it's not cycling, then I'm supposing:

The pilot lights.

The spark ignitor keeps sparking, often at a reduced rate once the pilot lights.

After 20-30 seconds or so the spark shuts off altogether.

Then the pilot burners shuts off and stays off until the thermostat is turned down and then up again.

Is that right? If not, please correct any discrepancy.

The pilot lights.

The ignitor keeps sparking...may slow down a bit once it lights (which is almost immediately)

After 20 seconds or so the ignitor shuts off.

You can hear the pilot gas shut off about 10 sec after the ignitor shuts off and then the pilot goes out.

The pilot (ignitor etc) stays off until I cycle the thermostat.
 
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Old 11-17-09, 08:57 PM
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Originally Posted by SeattlePioneer
Wow! I see you have the original valve manufactured in 1987! Usually those would have burned out LONG ago.

The replacement valves virtually never fail.


You may want to take pictures of a couple of the burners after you've brushed them off. Sometimes the burner ports can rust out and the burners would need to be replaced.

I can't seem to get pics of the burners too well without pulling them out... but they don't seem to be rusted out.

I do live in the high dez where we have VERY low humididy...<10% during the day most times.

Not much rusts here, but there would be the products of burning that would contribute, but to my eye they don't look bad.
 
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Old 11-17-09, 09:15 PM
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From your test, the hold coil (terminals 3-4) is burned out. That will cause the pilot to shut off. But usually it will relight when the pilot switch cools off and starts the ignition sequence again.


Your picture of the curcuit diagram isn't good enough for me to check it out in sufficient detail. If you'd like to take another picture emphasizing the gas valve connections (about the bottom 1/3rd of the diagrams) perhaps I can understand why it's not cycling.

But I'd start shopping for a new valve.
 
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Old 11-17-09, 09:59 PM
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Uploading pics now. will post shortly.
Do you know the replacement model # for this valve? I sure appreciate all of your help.,
 
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Old 11-17-09, 10:03 PM
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Old 11-17-09, 11:27 PM
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Thanks for posting the circuit diagrams.

Usually with a burned out hold coil, the pilot ignition sequence starts over again when the pilot switch cools off and again provides power to turn on the pick coil and the spark ignitor.

I don't see why it wouldn't do that customary routine.

Still, the key is the gas valve with the burned out coil that needs to be replaced.

Frankly, I recommend having a service agency install that for you. Correctly setting up the gas valve requires a measure of expertise, and you should have the burners pulled and cleaned and the heat exchanger inspected for cracks or holes.

At least you can impress the repairman by casually telling him that the hold coil on the furnace is burned out!

Sorry I can't be of more help.
 
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Old 11-18-09, 06:36 AM
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Thanks again for all your help. It's appreciated.
 
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Old 11-18-09, 06:51 AM
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It might be smart to double check the burned out hold coil by taking the wires off both the #3 and #4 terminals and checking continuity across the #3 and #4 terminals directly.

Removing the second wire shouldn't make a difference, but I'd still do the double check.
 
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Old 11-18-09, 04:22 PM
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Here is how I double check for a failed hold position:
Unplug the pilot harness at the pilot, Push pilot wire side aside and install a jumper in the opposing harness in the holes that represent green & yellow. That will start the ignition sequence, spark & pilot gas. After pilot has lit remove jumper and install in holes that represent yellow & white. If the pilot pilt goes out then I install the jumpers in both yellow/green & yellow/white. Now that will keep the pilot on and also energize the main valve operator and the burners will light. When you have to use two jumpers this proves the hold portion is bad. Seems like a lot of trouble, but why not be sure. Everything S/P has said is right on the money, don't be concerned about his knowledge.
 
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Old 11-19-09, 12:18 PM
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Ended up being a bad thermostat (I'd just replaced it last winter).
 
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Old 11-19-09, 02:18 PM
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Thanks for checking back.

Do you know what specifically was wrong with the thermostat?

And what about that hold coil? There must have been continuity across that after all?
 
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Old 11-19-09, 04:24 PM
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Originally Posted by rrwantr
Ended up being a bad thermostat (I'd just replaced it last winter).
Did you solve it yourself, or get someone? The reason I ask is that it was quite the leap to have been dicussing gas valve problems with the guys, and then suddenly solve the thermostat issue.

It is for reasons like yours that I like to see everyone check thermostats and pressure switches right off the bat. I was fooled once, for a while, by a stat acting up, when I thought there was no way the call for heat could be over with in seconds, yet it indeed was the stat! When something like that happens to you one time, you do not forget.
 
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Old 11-30-09, 05:30 PM
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Originally Posted by SeattlePioneer
Thanks for checking back.

Do you know what specifically was wrong with the thermostat?

And what about that hold coil? There must have been continuity across that after all?
There was not continuity across. I checked it multiple times.
No I don't know what was wrong specifically.
 
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Old 11-30-09, 05:34 PM
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Originally Posted by ecman51`
Did you solve it yourself, or get someone? The reason I ask is that it was quite the leap to have been dicussing gas valve problems with the guys, and then suddenly solve the thermostat issue.

It is for reasons like yours that I like to see everyone check thermostats and pressure switches right off the bat. I was fooled once, for a while, by a stat acting up, when I thought there was no way the call for heat could be over with in seconds, yet it indeed was the stat! When something like that happens to you one time, you do not forget.
Had someone come out as I thought it was the valve. He checked a few things and then looked at the thermostat. It was a model that he'd seen problems with on multiple units here in town lately. He believes it was a bad batch or something. He tried a unit he had with and that was it.
 
 

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