Atwood camper heater>>> repaired with pictures page 2

Hopefully your computer can't read and yours is an 8520. What is series II,III or IV?
Inspect the yellow wire between the circuit board and the flame sensor. Look for any nicks that would allow moisture or contact to ground.
Make sure the flame sensor is clean.
Manual says to inspect the exhaust and clean as #2 item. First item is to insure 11" column of LP supply
Have you cleaned the burner head? It is on right side in horizontal mount. Shut off LP, remove the gas valve ignitor assembly. The mesh burner assembly is connected to it. Use vacuum to clean out fire box. You can also use compressed air to knock debris loose and then vacuum again.
Adjust ignitor and flame sensor to 1/8th inch

Are you sure you have full voltage,the furnace will not fire if it senses low voltage. It will act just like you are describing.

At same time spark electrode is firing (click, click, click)the gas valve opens.

Main flame doesn't light because burner slots are obstructed, spark electrode gap is wrong (S/B 1/8"), spark electrode is not directly over center of burner slots or spark is going to ground thru cracked ceramic

IF main flame lights then it is not engulfing the electrode so no 'proving' signal is getting generated back to circuit board
Flame 'ionization' generates a small milivolt signal that goes back to circuit board proving main flame has lit. No signal so circuit board drops DC Voltage to gas valve closing it.
Crack ceramic, electrode not engulfed in flame, electrode dirty, wire connections dirty/loose/corroded

My heater was doing the same thing. Had to replace the circuit board, everything working fine now.

The board, if you are looking in from outside, is on the left, it does indeed flash a code, as I recall the code it will flash says "ignition lockout" which really does not tell you anything.

I had that same problem. here is the suspect list and what I found.

IN linear order:

Flame sensor (This is the rod that also generates the sparks)
Many have said if this gets a lot of carbon build up it may not get hot enough fast enough and will not generate the needed voltage to tell the control board "I"M HOT" (480mV or just under 1/2 volt) Mine tested good when I heated it with a volt meter attached.

Connections between flame sensor/spark rod and Control (Mother) board.
The voltage to generate that spark is on the order of 1,000 volts.. if the connections are not perfect that can punch right through, no problems.. As noted above the flame sense voltage is around 1/2. not so good at punching.

NOTE: Two connections (each end of the wire) plus the ground conections.

Control board:
My theory: On my Attwood the same wire carries both the kilovolt Spark and the half volt flame sense.. Well if the change over from SPARK to SENSE does not go well, or happens at the wrong point in the spark cycle (it is an AC voltage) then the flame sensor chip gets hit with up to 1500 volts, This is a chip designed to sense less than 1/2 volt, and we are going to shock it with 1500.. Not likely to survive. And Mine did not.

I ordered a New Dinosaur Boards board from American RV in California (not to be confused with American Rv in Michigan) and when I opened the box the very first thing that impressed me was the construction.l. Very solid, circuit board traces are larger and heavier and well soldered.. All connections looked very good to my trained eye.

Then on to the component side of the board... Well there is a component on the Dino board that is not on the OEM. it is a "Gas Discharge Tube" which is a commonly used device to protect against such things as lightening.. And from it's position, I suspect it is hooked to the flame sensor chip.. In short, it is there to prevent exactly what I think happened to my OEM board.. .And yours.

enblethen wrote:
Hopefully your computer can't read and yours is an 8520. What is series II,III or IV?

You were right, that by the time I walk from the camper to computer, I scrambled the number.
It is 8520 series IV
I took it apart and had small insects everywhere, but I believe those are still from Minnesota where I bought the camper 3 years ago.
Check the gas pressure and 3 burners on cooktop would not even blink when I started WH, so I assumed it had to have good pressure.
Washed circuit board and no kudos.
So finally start taking the furnace apart. Took some observation how to do it, so here are the pictures in case somebody has to do the same.
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After taking the cover off, you need to take off the wing nut visible on the center of the picture slightly to the right.
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Than in twisting motion, pull the exaust pipe out. Mine wasn't to badly corroded, but that might be hard part.
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Disconnect gas tubing. The bottom of the compartment has rubber seal, so I could push the tubing down for burner removal.
Burner assembly is hold by 3 screws with 1/4" hex head. One is above exhaust pipe, one you can see below the valve and 3rd one is next to #2
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This is the design where igniter and probe is the same thing. The thinner wire is ground. Lot of corrosion on wire mesh and some dead insects inside.
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Wire brushed the screen and blow the insects away.
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Clean burner goes back. Did the test and the flame stays on.
I clean everything, but my conclusion is that the rust on the burner screen made the flame too small and flame probe was not getting hot enough.
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Now I noticed, that the furnace is circulating camper air against steel cover. That has to lead to pretty good heat loss, so here is my improvement.
Thank you all guys for ideas.

BTW on picture 3 I see big hole on rounded plate, what looks like space for additional fastener.
I wonder if that was missing from the factory or PO did that.
I put it back the way it was and will not worry about it.

Well.... this morning the problem come back.
Yesterday it work on sunny afternoon, today it dies on cloudy morning.
Could it be the electronic board acting?

Wasn't there a plastic divider between outer metal door and fan assembly?
Did you clean the connectors on the circuit board? Yes, it could be defective circuit board. Look at your water heater to see if it is the same board. If so switch them out. If you decide to get new circuit board get a Dinosaur electronics version.

enblethen wrote:
Wasn't there a plastic divider between outer metal door and fan assembly?
Did you clean the connectors on the circuit board? Yes, it could be defective circuit board. Look at your water heater to see if it is the same board. If so switch them out. If you decide to get new circuit board get a Dinosaur electronics version.

A circuit board from a water heater is "instant fire." Don't use that on a furnace. There is a delay on the furnace board before ignition so the combustion fan can clear the system of any excess propane so you don't get an explosion.