I'm assuming you mean a 'electric' Water Heater switch?
Do you have two switches - one for Elec and one for Gas?
Does the water heater already work on Gas/propane?
if using the 'Electric' switch,
You must also be plugged into Shore Power, or have the Generator running for it to work
and, depending on your brand/type of water heater, it may have an outside 'elec' switch on the heater panel itself, that must also be ON
'14 Thor Palazzo 33.3 compact diesel
KingTailgater2 Dish, 100w/5amps roof SOLAR, BlueOx, 100,000+mi since '14... US, Alaska, and Canada... GA, NC, now N AL : )