melissa-is this an "on-demand" tankless type of water heater?

In my experience a piezo button clicks once to cause a spark...
and you need to be pushing down the gas button to supply fuel
when the spar is generated...

sometimes the device will not automatically allow the fuel to flow
until a sensor had detected sufficient heat--this is a safety feature
so that if the pilot light goes out the gas will turn off..

I had a Bosch Aquastar for many years...and the flame comes on when water flows thru....so you might want to open a faucet to flow h20
so that the heater will kick on....let us know how you do with this.

it is not rocket science. is there a little window where you can
see the spark or the flame? do you have propane or natural gas?
is the orafice correct for the type of fuel you use?
(have you used this before or is it a new device?)

Tankless/on demand water heaters are the best kind...
the ones that keep a tank full of water hot whether you
are using any or not seem quite wastefull.

here is a place to find service manuals and other info
http://www.bosch-climate.us/Bosch-Hot-Water/