Atwood heater failure - need advise!

wa8yxm wrote:
You may find this helpful... Note to others.. I typed this from memory the first time (Finally saved it to HD) if you find any errors or omissions, please call them to my attention so I can fix it. Thank you.

When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignights (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)

*: At nearly every step the control board is invovled. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.

1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid
4: .1: Bad ignition curcuit (high voltage) on control board. .2: Points too wide (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.

* applies to all steps nby the way So does bad wire/connection.

You MISSED the most important part. AFTER the 12 volts flows from the sail switch it goes THRU the Hi Limit switch. IF the Hi limit is bad(open) NOTHING happens. Main Control boards rarely fail anymore. Regardless of what some think. I cannot remember the last time I replaced a control board on a Furnace/Water-Heater-Refer. I HAVE replaced various control parts on these appliances, but rarely a control board. Doug