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Old 02-03-2023, 10:56 PM   #1
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Why is Propane Igniting at the Air Shutter on an Atwood G6A-7 Water Heater?

I have a circa 2015 Atwood G6A-7 (LPG only) hot water heater. For a couple years, I've been chasing a problem where propane incorrectly ignites in the main burner tube just past the air shutter opening and creates a pulse jet engine or sputtering sound.

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Here's a video of this problem: https://tv.gab.com/channel/robertkno...049d87d2a5a946

Things I've done:
  • Thoroughly cleaned the original main burner, orifice, pilot, thermocouple, and U tube through the tank.
  • Adjusted the air shutter ad nauseum.
  • Installed a new main burner and orifice.
  • Adjusted the RV's main LPG low pressure regulator to ensure at least 11" WC at 50% dynamic load.
  • Verified RV's main LPG low pressure regulator lock-up pressure was below 14" WC (i.e. the regulator is working properly).
  • Verified at least 11" WC operating pressure at the test port on the Robertshaw 91602 gas valve.
  • Perfectly aligned the output elbow and orifice with the main burner to ensure smooth gas flow.
  • Checked for leaks on all fittings.
  • Verified proper propane operation on furnace, fridge, and stove.

Yet the brand new main burner (and orifice) still turns into a pulse jet engine wannabe when it ignites.

Interestingly, even though I am at sea level, I can't close the air shutter far enough to receive a too-rich (yellow) burn. In other words, even with the air shutter completely closed, it still seems to be burning a touch too lean. This video demonstrates that:

https://tv.gab.com/channel/robertkno...7f930a185988fb

This leads me to believe that I'm not getting enough gas volume and/or pressure through the gas valve and the main burner. This, in turn, means that the flame can burn back down the main burner tube and ignite at the air shutter. It is as if the volume and/or pressure isn't high enough to keep the flame pushed out the end of the main burner. (A good analogy is a cutting torch and how far the ignition is away from the tip depending on how far one turns up the valves.)

Yet with measured good pressures, I'm at a loss for what to check next. Any ideas?
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Old 02-04-2023, 07:40 AM   #2
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First video, too much primary air.
Second video, too little primary air.
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Old 02-04-2023, 08:06 AM   #3
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Quote:
Originally Posted by TandW View Post
First video, too much primary air.
Second video, too little primary air.
Yes. In the first video, it was burning too lean even with the air shutter closed as far as possible.

In the second video, it burns close to correct (but still a little lean) in the first part of the video with the air shutter closed as far as possible. Then, when I cover up an additional part of the air shutter with my finger, it begins to burn too rich. I did that to demonstrate how I'm not able to make the flame burn rich even when the air shutter is closed as far as possible unless I cover up an additional part of the air shutter. In ever other video I've seen of every water heater, users are able to get a too-rich burn by closing the air shutter as far as possible.

In other words, my air shutter and circumstances don't seem to give me enough range to adjust the burn properly. Since the original and replacement main burners are Atwood products, that leads me to believe that I'm not getting enough gas or pressure through the burner despite the correct pressure readings.
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Old 02-04-2023, 10:55 AM   #4
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I think I may be starting to have the same problem. Chuck
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Old 02-04-2023, 11:09 AM   #5
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Stay tuned

A fine gentleman by the name of Old-Biscuit will be along to help you out.
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Old 02-04-2023, 01:17 PM   #6
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Possible Debris inside Valve

I read this gentleman's experience about having dried pipe dope debris inside the Orifice Holder (the name Atwood gives to the 90 output elbow) and inside the valve body.

https://www.airforums.com/forums/f44...ng-219946.html

I did indeed have a couple small pieces of debris and some fine white particles inside the valve body.
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I cleaned everything up and blew out the valve body with gentle compressed air. I also cleaned up the main burner yet again. While the burn still seems to be a touch lean even with the air shutter closed as far as possible, perhaps that debris was responsible for intermittent gas flow through the orifice, which in turn caused the pulse jet sputtering. I'll monitor. If it's going to happen again, it usually happens within a couple days.
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Old 02-04-2023, 01:47 PM   #7
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Remove orifice
Soak in alcohol
Air Dry........no poking/no air pressure---those can damage the metered hole
Blow out gas valve with LOW air pressure.....less then 0.5 psi (Max rating of valve) with orifice removed

Sputtering/blowback ---dirty orifice
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Old 02-05-2023, 06:53 PM   #8
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Quote:
Originally Posted by Bob K. View Post
I read this gentleman's experience about having dried pipe dope debris inside the Orifice Holder (the name Atwood gives to the 90 output elbow) and inside the valve body.

https://www.airforums.com/forums/f44...ng-219946.html

I did indeed have a couple small pieces of debris and some fine white particles inside the valve body.
Attachment 385759

Attachment 385760

I cleaned everything up and blew out the valve body with gentle compressed air. I also cleaned up the main burner yet again. While the burn still seems to be a touch lean even with the air shutter closed as far as possible, perhaps that debris was responsible for intermittent gas flow through the orifice, which in turn caused the pulse jet sputtering. I'll monitor. If it's going to happen again, it usually happens within a couple days.
Well THAT didn't work. It started sputtering again within about 6 ignition cycles. This time I:
  • Disconnected the propane hose at the main regulator and at the input to the Robertshaw gas valve & blew compressed air through it to make sure it was clear. No problems.
  • Checked the length of the propane hose to make sure it wasn't kinked. No problems.
  • Cleaned all of the old pipe dope out of the threads on the gas valve inlet.
  • Gently blew air into the inlet and vacuumed it to clear any potential debris. Unlike the gentleman from the Airstream forum mentioned above, my gas valve has no inlet debris screen.
  • Cleaned the orifice and main burner yet again.
  • Ensured the orifice and main burner were very closely aligned, again.
I was running out of things it could be, so I rechecked and then adjusted the main burner pressure. This entailed removing the cap, digging out the red factory sealant, and adjusting with a straight screwdriver bit. With two propane services in operation, it was running a bit low at about 10.6" WC. I adjusted it up a bit so that it was at least 11" WC while two gas appliances were in operation.
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I also lengthened the screw slot in the air shutter so that I could close it just a touch more. This required futzing around with the main burner bracket a bit so that the air shutter wouldn't slide off of the Orifice Holder when the air shutter was closed a bit more. Whatever the reason -- alignment, incorrectly installed by Jayco, etc. -- I've never been able to close my air shutter as much as folks do in all the other videos I see. As a result, it always seemed to run lean at sea level even with the air shutter closed as far as possible.
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Now I'm able to put the air shutter at about 1/4 open, and I can easily close it far enough that I get a rich, yellow burn. Couldn't do that before.
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So far, I've got a nice, quieter blue burn with just a touch of yellow. It usually takes 6 or so cycles before the sputtering occurs, so we'll see if I fixed it this time.
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Old 02-09-2023, 09:01 PM   #9
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Quote:
Originally Posted by Bob K. View Post
Well THAT didn't work. It started sputtering again within about 6 ignition cycles. This time I:
  • Disconnected the propane hose at the main regulator and at the input to the Robertshaw gas valve & blew compressed air through it to make sure it was clear. No problems.
  • Checked the length of the propane hose to make sure it wasn't kinked. No problems.
  • Cleaned all of the old pipe dope out of the threads on the gas valve inlet.
  • Gently blew air into the inlet and vacuumed it to clear any potential debris. Unlike the gentleman from the Airstream forum mentioned above, my gas valve has no inlet debris screen.
  • Cleaned the orifice and main burner yet again.
  • Ensured the orifice and main burner were very closely aligned, again.
I was running out of things it could be, so I rechecked and then adjusted the main burner pressure. This entailed removing the cap, digging out the red factory sealant, and adjusting with a straight screwdriver bit. With two propane services in operation, it was running a bit low at about 10.6" WC. I adjusted it up a bit so that it was at least 11" WC while two gas appliances were in operation.
Attachment 385855
Attachment 385856

I also lengthened the screw slot in the air shutter so that I could close it just a touch more. This required futzing around with the main burner bracket a bit so that the air shutter wouldn't slide off of the Orifice Holder when the air shutter was closed a bit more. Whatever the reason -- alignment, incorrectly installed by Jayco, etc. -- I've never been able to close my air shutter as much as folks do in all the other videos I see. As a result, it always seemed to run lean at sea level even with the air shutter closed as far as possible.
Attachment 385854

Now I'm able to put the air shutter at about 1/4 open, and I can easily close it far enough that I get a rich, yellow burn. Couldn't do that before.
Attachment 385857

So far, I've got a nice, quieter blue burn with just a touch of yellow. It usually takes 6 or so cycles before the sputtering occurs, so we'll see if I fixed it this time.
I think that did it. By ensuring that the trailer's main low pressure regulator was at least 11" WC at 50% load, and then adjusting the Robertshaw gas valve to be at least 11" WC with two propane devices in operation, I'm now getting a much gentler, blue burn with no pulse jet engine (or sputtering) problems.

Whether the Robertshaw's main burner pressure wasn't set correctly at the factory or the valve has worn over time, I don't know; however, upping the pressure to the correct value appears to have solved the problem. It looks like low pressure (and a resulting lack of adequate propane volume) was resulting in a lean burn that caused sputtering.
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