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Old 02-23-2013, 04:57 PM   #1
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Atwood DSI WH problem

I have the Atwood MPD 93756. It works just fine on shore power. Not so well on LPG.

Everything is is order, as far as I can tell. Problem is... the burner produces flame while the electronic igniter is sparking. Once the igniter finishes it's cycle, the pretty blue flame goes out. The gas supply is immediately cut when the igniter stops. Whatever it is that tells the gas valve to open and the igniter to spark is not talking to the gas valve after it tells the igniter to quit sparking.

I've bypassed the cutoff switch to determine that is not the problem. What do I need to look at next?
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Old 02-23-2013, 05:24 PM   #2
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Is there a thermocouple that the flame heats that tells the gas valve that the gas lit and is ok to keep the valve open?

Maybe the thermocouple is not located in the flame. They can easily be moved slightly to be in the right spot like bending wire.

I've also read where the TC gets corrosion on it and can be cleaned with scotch-brite.

Could be one of these possibilites.

Keep us posted,
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Old 02-23-2013, 05:43 PM   #3
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Thanks but no thermocouple on a DSI.
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Old 02-23-2013, 06:12 PM   #4
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Hmm,
you would think something has to sense flame is lit.
Is there an electrode? Maybe this is what people are cleaning with scotch-brite.

Sorry, not very much help here.

Someone else should chime in.

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Old 02-23-2013, 06:21 PM   #5
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There is an electrode at the end of the burner tube. This sparks when the switch is activated inside. The spec for the sparking cycle is "6 to 9 seconds" Once the sparking begins, the burner flame ignites instantly but the instant the electrode quits sparking, the burner flame goes out. Makes no sense at all.

My refrigerator and furnace also have auto ignition and they work just fine.
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Old 02-23-2013, 06:54 PM   #6
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http://bryantrv.com/docs2/docs/atwoodwaterheater.pdf

Sounds like the elctrode provides the spark and also has a built in flame sensor.

there's some other safety features in this troubleshooting guide. I am not familiar with them, but it may make sense to you with the unit in front of you.

I was reading the section for heaters with DSI.

Wish I could be of more help.

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Old 02-23-2013, 07:25 PM   #7
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Thank you Doug. That was a lot of help.

Your comments on the flame sensor and the scothbrite pad made me understand something that didn't register before. I'll check out the electrode more closely tomorrow. Maybe it's too crusty to sense the flame.

I'll let you know how it goes.
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Old 02-23-2013, 07:35 PM   #8
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Wil,
I believe that is what some people have experienced.
The flame sensor can get oxidation on it acting like an insulator.

Hopefully you'll get it working.

Kind regards,
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Old 02-24-2013, 10:50 AM   #9
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Quote:
Originally Posted by A32319 View Post
Thanks but no thermocouple on a DSI.
Something has to tell it the flame has gone out or the gas would continue to flow... I am sure this is where your problem is..
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Old 02-24-2013, 12:50 PM   #10
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Well, I cleaned the electrodes. They were not bad at all. No change in operation. Once the sparking quits, the flame quits and the thing goes into lockout mode. The lockout light on the control is doing what it's supposed to do.

Could be the flame sensor part of the electrode isn't working. Also could be the flame isn't running long enough to heat the sensor and override the lockout. The flame runs only 5.3 seconds while it's supposed to run 6-8 seconds. This is reflected by the lockout indicator light. You can time it by the flame or the lockout light. I suppose it could also be the continue-to-run side of the dual solenoid gas valve is bad or electrical signal to make it stay open.

I guess it will take me some time to sort it out. I hate to start throwing parts at it until I know what's wrong. It's probably not all that complicated for someone fluent in DSI... but that ain't me.
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