Atwood 8525-IV-DCLP Furnace lights, burns, but goes out, won't stay lit, repeat

Hi Everyone,

I am writing in hopes that someone can help me with the following Atwood Furnace issue (I have a call into Atwood but they are closed).

Model - 8525-IV-DCLP, this is installed in a 2012 Coachman Freedom Express.  The install is only 4 years old - but expired warrantee.

Orignial issue:  Furnace began not wanting to ignite on a consistant basis.  Seemed to run ok for a time (like several hours) but wouldn't fully cycle correctly.  Eventually, it stopped lighting and wouldn't restart.  Trouble shooting showed that I had an ignition failure according to the LED on the control board.  What I did to attempt to correct the issue:

1. replaced the thermostat
2. replaced and adjusted the campers gas regulator (purchased an upgraded model - Cavagna 52-A-890-0006C)

Tested - would not ignite at all - just fan - no electrode snapping - no fire.  LED still indicated ignition fault.

Next steps attempted:

1. Replaced Control Board

Same results as above.  No ignition, no flame, LED indicated ignition failure.

Next steps attempted:

1. Replaced Gas valve
2. Replaced Electrode
3. Replaced Sail Switch (it tested good but had a new one so I changed it).
4. Replaced the burner (yes...just thought it was a wise idea if I was taking the older one out.
5. Verified Gas Pressure at the inlet (from the camper regulator) - 14 in.H2O.  Verified with stove running at 12 in.H2O (both above minimum spec)
6. tested all grounds (all tested good), tested all connections to the board (PINS).

New but strange Result: Furnace fired up - but only runs for about 2 seconds, shuts the gas valve, flame goes out, then re-ignites, burns 2 seconds, goes out, and repeats this cycle without stopping the fan.  I let it do it for about 5 min or so just to understand what I was hearing.

Next steps:

1. Replace limit switch
2. check jet - all clean (checked it before but just to be sure again).

Result: No change from last time - Furnace fired up - but only runs for about 2 seconds, shuts the gas valve, flame goes out, then re-ignites, burns 2 seconds, goes out, and repeats this cycle without stopping the fan.  I let it do it for about 5 min or so just to understand what I was hearing.

Pulled the furnace out again - checked everything - put new board back in, verified all connections, grounds, etc.  Same result.

So the full list from start to finish:

1. Replaced Camper Gas Regulator - adjusted to spec at the furnace (14 in.H2O with nothing running, 12 in.H2O with everything running).
2. Replaced the Thermostat with an Atwood exact model replacement. (it is set at .43 Amps)
3. Replaced the control board
4. Replaced the ignitor
5. Replaced the gas valve/regulator in the furnace
6. Replaced the Sail Switch
7. Replaced the Limit Switch
8. Checked all grounds
9. Purged the gas system (many times)

At this point I have no more things to replace.  I am completely out of ideas.  I know there are some very smart folks on this board so I am hoping someone will take pity on me and come up with something I may have missed or don't know to check.  Thank you all in advance for reading and if you have a possible solution, I am totally open to trying anything.  Please help me. 

Whoa!  You threw way too many parts at it. Many of those things are not even related to the problem.  You seem to have already replaced every single component except the outer case and the case valve, but I don't think it is those either.

"Ignition fault" simple means what you already knew: it did not light when requested. The most common cause is failure for the "I'm lit" signal to get back to the control board. Without that confirmation, the furnace shuts down (to prevent a possible gas explosion). That problem is often a corroded wire connector or maybe even a broken wire. Next is a faulty sensor (which is also the igniter).

I also think your gas pressure is too high - I would not exceed 11 WC inches at the furnace. Not sure what effect high pressure might have, though.

You can eliminate the thermostat from the picture by simply jumpering +12v to the control line to the furnace. That calls for heat and will make it attempt  to fire up. I don't think the thermostat has anything to do with those symptoms, though.

Can you measure the voltage feedback to the controller after ignition? Or apply a very small voltage to fake it and see if it keeps running? See the Atwood Service Manual for details on the flame (ignition) sensor. Get one here if you don't have it.
http://bryantrv.com/docs.html

Might also find some basic help info in this article: http://www.rvforum.net/miscfiles/Furnace_Trouble-2.pdf

WOW, You shure replaced a lot of stuff. In fact dang near everything except the control board.

When I had that same set of symptoms I ran a whole bunch of diagnostic tests, Verified everything you replaced was good. (Which you did the expensive way) Contacted American RV in California and had them send me a band new Dinosaur Boards control board.

When it arrived (I thinjk it was like 127.00 delivered) a few days later I opened the box and looked at it,, Was very impressed with the quality of the product... I have a theory as to what killed my (and your) original board.. Dinosaur boards it seems shares myu theory because there was a lovely little protection device (Gas discharge tube) designed to prevent just that from happening..  Plugged it in and AHH.. Blessed warmth ensued.

Included in the story above is my recommendations.. NOTE: You may find that board closer to home (As in at a local RV store)  But Dinosaur boards make very solid products.... Far better than the original.

I think he said he replaced the control board.

Thank you to everyone who have replied. 

I feel the same way as many of you have pointed out - I think at this point the only parts I have not replaced is the case and the combustion chamber.  Let me back up however (I was typing in a frustrated state).  Each part was changed based on advice and troubleshooting one step at a time (some were changed together simply because I was in that area of the furnace. 

Gary - I am also wondering about the gas pressure being higher than 11 WC.  Everything I read indicates that I must have a minimum of 11 WC but as far as I see nothing says there is a maximum (or a acceptable range).  After sleeping on the issue, my thought is this - could I have good pressure but poor rate of flow?  I don't know a way of measuring flow at my disposal.  I totally agree - I have changed every electrical component only to have it present with this new issue of run, ignite, burn, go out, repeat. 

Would this make sense - I will get two new bottles of gas (I have swapped the bottles and they are over half full at this point but I think I want to try new ones).  Disconnect the lines under the camper and clear them with compressed air to ensure they are full flow?

John - I am not opposed to getting a Dinosaur Board (I ordered an exact replacement from Fenwal).  But at this point, another $127 bucks has my wife about ready to smack me. 

Thanks everyone for the ideas and discussion.  I truly appreciate the help.

A new furnace would have cost $485.00.  http://www.amazon.com/ATWOOD-FURNACE-8525-CAMPER-HYDROFLAME/dp/B014JX0X28

Hope you find the problem.

Thanks Rene - That's what I have been working from regarding cost.  So far I am only about $200 into parts - but at this point, I won't spend more $$.  Just need to understand the issue better since all the parts are now testing fine.  Honestly at this point, replacing the entire thing won't likely fix the issue if it's gas supply in nature.

Can anyone weigh in on the pressure at the line and possibly the required flow rate?  and how i might test this?  or even pointers on ensuring I do indeed have a clear and functional line from the tank?

Thanks again to everyone for reading and responding. 

Air bubbles in the gas line could disrupt the flame, as could gunk that halts the flow. A partial blockage could let enough gas seep by to allow ignition, but not allow it to replenish adequately, so that the flame dies. 11-14 WC inches isn't much pressure (about 0.5-0.7 psi), so it doesn't push stuff out of the way readily. Usually a clog in the gas lines is a total blockage, but it doesn't have to be. Clogs come from oily globs that can build up in the LP tank and they can sometimes work their way into the gas lines, especially if the tank is run down to empty. Purging the lines would be worth a try.  Or make a test run with a different tank plumbed direct to the furnace valve (with a regulator, of course) to see how that works.

I agree the Atwood manuals don't show a high limit for LP pressure, but a system pressure of 11" WC is the standard for all LP appliances. There is no benefit from over-pressure, but maybe no harm either (as long as it is reasonably close).  I've not seen a spec for flow rate anywhere, but furnaces will go out if the supply in not "adequate".  They are also very sensitive to the combustion air intake & exhaust, and anything that disrupts the flow through those tubes can also result in the oddball symptoms you have. Makes sure those tubes are free of rust flakes and critter nests, and that the gaskets are in good shape.

I went through all the same steps with no results.  Had to figure the gas PSI was the issue. Did not have a manometer so changed another part.  The propane tank switch over valve also has a regulator which I figured was the problem.  Put in a new valve and furnace worked like brand new.

The higher pressure could be blowing the flame front out past the electrode, preventing the flame sensor from generating the needed millivolts for the control board. Or the electrode is not properly gaped and positioned in the flame.

My Atwood 8535 cycles on and off 3 times before giving up.  I turn down the thermostat and back up and, after a few times, it works.  This happens usually after a rain.  The burner does light on each cycle.  It?s almost like something like a connection gets dried out by the heat from the repeated failed starts and then it works.  Other times, it works fine.  I?ve tried to jiggle the wires and connectors but it seems like the repeated lightings is all that works.  Any suggestions?

This is a nearly 5 year old post. Will the new members start a new post detailing exactly what your issue is and what you?ve done. It will save everyone from reading this entire old post.