attwood water heater

enblethen wrote:
Detail 12 shows wiring for combined LP-DSI and 120 volt water heater. 12 volts goes to the switch before water heater.Atwood manual

YES 12V DC comes from DC Dist Panel (FUSED) to switches and then goes to the circuit board (electric/white wire & gas/orange wire) then from circuit board it goes to 'thermal fuse' to normal t-stat and then back to circuit board (brown wire)

It maybe present at circuit board but IF thermal fuse is blown that is end of operation for either electric or gas.

Easy to test right at circuit board for 12V DC with either/both switches on

Detail 12 shows wiring for combined LP-DSI and 120 volt water heater. 12 volts goes to the switch before water heater.Atwood manual

As Chris suggested.........check that thermal fuse
It's a one shot fuse that trips on flame blow back. When it trips ALL 12V DC power is tripped so WH will not operate on electric or gas due to the use of common t-stats

Provided this WH is in your 2005 Newmar or the 2007 Dolphin and not one of the older RVs you have listed

What is the exact model number of your water heater? It should be shown on the exterior access frame.
Some models use 12 volt control for 120 volt operation as well as the LP function.
Make sure you have 12 volts to the switches.

I would test for 12 volts through the front mount thermostat and flame fuse-