Furnace issue

Hi There:
I have seen this issue being discussed in few forums and it seems there is a furnace issue diagnosis  thread some where here but unfortunately I cannot open the page, it cold be due to our limited internet and connection type since we are on the road currently.
Here is the issue on 2016 Thor class C with Atwood Hydro flame. I don't know the exact model # but what I see on the furnace and circuit board are 30575 and 30319. The issue is the fan keeps going and the ignitor tries to kick on but nothing happens. On few occasion I see a spark/flame through the exhaust pipe but again the system fails to stay on. Based on the system booklet, there is an LED light which suppose to flash and give some indication about the where the problem can possibly be, but that LED light is not flashing at all. I have been reading as much as I can while we are on the road, I have cleaned the ground connection although non of the connections look bad, the propane tank is 70% full and stove and refrigerator don't have any issue functioning. I read a lot about circuit board failure but I want to know if there is anything I can do on the road or if I need to order a new circuit board.
If this is propane flow issue, how can I purge the lines at the furnace?
Thanks for all the help. Yellowstone got the now couple of days ago when our furnace failed!

Try this link and scroll down to hydroflame furnaces. There are several service manuals that should help you troubleshoot the problem. Good luck. Must be chilly in Yellowstone by now.

Thank you for the link. I will read through them but it seems my unit model is newer than what it has listed. On the manual booklet it says: Hydro flame AFM series (AFMD 16, 20, 25, 30 and 35).
I called Thor and they say take it to dealer. What else can you expect?! I called Atwood, and their number has changed!
Yes, it was very chilly, 28 degree F chilly for summer!

The AFM series Atwood isn't notably different than their other DSI ignition models. The operating principle is the same, as are the red light fault codes (but you don't see any).

If the igniter clicks but the furnace fails to light or remain lit, you would typically see a flame sense fault on the red light, two blinks repeated at 3 second intervals.  The most common cause for no-ignition is a partial blockage in the air intake and exhaust tubes, e.g. spider webs, mud dauber nests, rust flakes, etc. It doesn't take much to disrupt the smooth flow of air in/out and cause non-ignition.

I won't say a board fault cannot happen, but it would be far down on my suspect list, especially since it is a 2016.

Look at your furnace board to see if it is or has been wet, especially if the the furnace door has the louvers that go inward, instead of poking out. Mine had the louvers like that. Coachmen/Atwood sent me a new door, door frame, exhaust flue, and board free of charge.

I hate to state the obvious, is the propane sniffer working??

Thanks guys.
How do I check/clean air inlet/outlet? The vent/exhaust pipe is clean since I have taken that off few times to get the cover off.
I don't see any evidence of moisture on the board but, yes, the cover is the type that can direct the water inward rather than outward. I was very shock to see the design specially when I saw the board is sitting there with no cover on it.
What is the propane sniffer? The thank is almost full. Also, on two occasions, I saw (smelled the propane at the vent/exhaust pipe) an ignite of propane but the system didn't maintained it.

Can somebody tell me where the fail safe switch is? I called Atwood this am and the lady on the line said it sounds like fail safe switch. Of course she recommended to take it to dealer and of course she said our unit just came out of warranty!
The picture below is what I see when I take the cover off. To be honest looks like a mess for and electronic board and so many wires being away from elements with a just plastic cover. Where is the fail safe switch is located? The blue wires are connected to igniter, I assume, The gas regulator is the obvious one in addition to vent/exhaust tube (sorry, I don't know what exactly called) and the circuit board.
Thanks again.

What is the propane sniffer?

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I suspect that whokares2 means the propane detector and I think he is alluding to the older type that was associated with a propane cutoff valve. Yours likely does not have that feature being in a 2016 unit as that feature was largely discontinued in the mid 90's. That said, try turning the propane supply off at the tank and them SLOWLY open the valve again. The tank valves have a built-in cutoff system that will cut off the propane supply should the valve suspect a leak is present, perhaps caused by in very high inrush of propane to the system. Light the stove and get a good blue flame and this should purge the system of any air present. Then, try the furnace again.

The 'failsafe ' switch could be the sail switch. This switch prevents the furnace from lighting should the airflow be deemed inadequate. There is also a limit switch located in the chamber (heat exchanger) which will prevent the the furnace from firing.

Can somebody tell me where the fail safe switch is? I called Atwood this am and the lady on the line said it sounds like fail safe switch.

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Hmmm. Not a term usually applied to RV furnaces, so surprised to hear it from an alleged tech rep.  There are various fail-safe mechanisms in a furnace where that term could apply:
1. Fan sail switch - makes sure the fan speed is adequate for safe operation
2. Flame sensor - verifies that the burner is lit and shuts gas off if not
3. High Limit switch - shuts burner off if the combustion chamber overheats

What you described here does NOT sound like a "fail safe" to me.  Take a look at my treatise on Furnace Troubleshooting. It's pretty much generic for all DSI type RV furnaces and cover the main components and how it all works. It's in the RVForum Library.
Furnace Troubleshooting

If the sail switch opened, the igniter would not spark. Nor would it spark if the High Limit switch opened. The flame sensor probably did trigger a shut down, as it is supposed to do if the burner doesn't ignite after three tries, but that's not a "fault". It's "working as designed".

 

Most RV shops have an Electronic Board Tester...Some will check your board at no charge... if you take it out and in to them.

How do I check/clean air inlet/outlet? The vent/exhaust pipe is clean since I have taken that off few times to get the cover off.

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Since you have the tube off, you can probably see through it and/or blow it out. There is a short stub where it attaches to the combustion chamber, but that is usually OK unless very rusty inside.

Thanks for all the info. We have landed at Moab today. In few days we headed for LA/CA so I hope there is no need for furnace until then. We will be in LA for couple of weeks with family and friends and I will check everything out and report back. I will try the propane suggestion as mentioned but how can I check the fan to see if it creates enough air flow? Just check its input electrical voltage?

On my other computer I have a diagnosis procedure.. It has been posted to the forum more than once however and is based on a combination of forum posts (This and other) and personal expermentation and procedure... I will try to do most of it from memory

When the thermostat calls for HEAT
The control board on the furnace is the conductor, it directs all actions.
1:Start fan
2: Start generating sparks and open gas valve
3: Wait a few seconds
4:Stop sparking and read flame sensor (See note)
5: If flame sensor NOT HOT, close gas valve and go to step 1 (Fan continues to run)
After 3rd loop if still not hot go to LOCK OUT and flash LED

If hot: Continue operation till T-Stat says "Warm enough" then shut off burner and a bit later blower and await next call for HEAT

Possible issues: At all steps the control board..  See notes
Flame sensor so dirty that it does not get hot enough fast enough
Out of propane
Clogged oriface not letting propane pass
Bad solenoid
Bad connections.

NOTES:
On my Atwood it is a "Single wire ignition" this means the same wire that carries like 1,000 VAC to make sparks also carries the less than 1/2 volt DC produced by the flame sensor (480mV) Imagine what happens if the change over goes wonky and that sensor chip gets hit with over 1,000 volts peak of Spark Power (OUCH).
This is what I believe happened to my control board.

Based on reviews and posts in the forums I ordered a Dinosaur Boards Replacement for my Atwood

Now.. .I am a trained electronics technician, Have certificate and everything, plus nearly 50 years (49 to be exact) as a licensed ham radio operator..

I opened the box and looked at the Dino board.... "Dang this thing is well built"

I then looked closer.. I noticed a part not on the Atwood board.. this part is a Gas Discharge Tube, this is a type of voltage spike supressor... It was mounted next to the flame sensor chip.. Humm. WOnder if Dino boards thinks like I do as to what killed my OEM board?  Sure looks like it.

That was in 2011.. RV is a 2005. Do not know exactly when the board failed (Likely 2010 as I had issues back then)  Furnace not working just now but for other reasons.. I'm repairing something nad have the propane turned off. If I need furnace (90 degrees here in Eastern lower MI today) I need only open Propane valve.

but how can I check the fan to see if it creates enough air flow? Just check its input electrical voltage?

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There will be a microswitch with a paddle on its lever-arm that sits in front of the fan, called a "sail switch". The fan has to move enough air to push the paddle over and close the switch. If the fan speed is adequate, it will.  That switch then provides power to the ignition control circuit board, enabling the ignition process to run. If your board is triggering sparks at the igniter, you know the fan speed is adequate and the sail switch is functional.

Hi again:
This is an update on my furnace issue. We have been in Socal for a week now and beside seeing family and friends I was doing some more reading on the furnace issue that I have since I have a good cable internet connection now. This board has great furnace trouble shooting thread, thank you.
Now this is the problem that I found: furnace is back to normal in warm Socal, it is coming on with the first try!!!Any ideas why it didnt work at cold temperature? The RV has been parked in storage facility and the furnace runs fine on house batteries. I can't think that the site electrical connection could have anything to do with it since the furnace runs on 12V. What can I trouble shoot?