Piolit is lite but not fireing up to heat water!

Sounds like the thermocouple has gone bad. Thankfully it's a cheap part that is replaced easily. If it were me I'd replace the thermocouple and see if that solves it.

Here's a "how to" on replacing the thermocouple:

How to Change a Thermocouple on Your Gas Hot Water Heater - Associated Content (http://www.associatedcontent.com/article/584031/how_to_change_a_thermocouple_on_your.html)