Follow these steps to identify the correct version for your heater
Locate the identification Sticker on the back of your heater unit. It should contain Model information and a Serial Number.
Compare your Sticker to the examples below, and check your Serial Number (SN) prefix to determine which version you need.
If your Sticker looks like this appearance :

When ordering, select Version 1.
If your Sticker looks like this appearance :

When ordering, select Version 2.