Furnace Burner Keeps Cutting Off

wolfe10 wrote:

Old-Biscuit wrote:
This was posted in another RV forum by 'A1RVTraveler'

I am a mobile RV tech and I am going to suggest something you need to try.

The 2017-2019 Dometic Atwood furnace has been experiencing some problems with sail switches not staying closed during furnace operation. This has been especially problematic with furnaces mounted vertically.

A new sail switch was introduced that has cured the problem.

This is how I troubleshoot.

Removed the sail switch and bracket from the furnace. Leave all wires connected.

Have someone turn on the furnace.

Once the motor starts, close the sail switch with your hand and keep it closed.

If the furnace ignites and runs fine, the sail switch needs to be replaced with the new style switch.

You can not close the sail switch until the motor starts.

Let me know what happens.

Matt

PS:

The new sail switch comes with a modified bracket to allow the sail switch to travel an extra 1/32". Seems odd, but this cures the problem. The actual sail switch in not bad, just not staying closed during operation.

This only applies to 2017-2019 Dometic-Atwood furnaces with straight blade sail switches, not the angle bent sail switches.

See post #28

Not sure I go along with this one as first thing to check. Could the sail switch be faulty-- certainly.

But, remember what it does for a living-- it VERIFIES proper air flow for before allowing the furnace to ignite.

So, start by verifying that the air return to the furnace is not blocked, all ducts in good condition (not crushed) and all vents open. Also a good idea to check from the outside for dirt, mud dubbers nests, etc before firing it up for the first time of the season.

If all the above are good, connections to the PC board good and clean (or use DeOxit to clean the connections) THEN suspect the sail switch.

The issue is the Straight Blade paddle sail switch 'flutters' causing micro switch to open/close...which drops DC and then passes DC so circuit board drops DC to gas/valve then energizes gas valve...flame on/off/on/off

Bent paddle sail switch has slightly move upward movement which holds micro switch CLOSED...no 'fluttering'

Simple check of which style paddle...straight or bent and voila ---issue IDd