Designing Kitchens and Bathrooms - remove old grout

Is there a machine that I can use to remove old grout from bathroom tile. We have a leak in the ceiling below our bathroom. We have tested the shower pan and don't think the leak is coming from there. We had to take down the drywall in our bedroom to see if the piping was causing the leak. But no evidence from there. It appears that the water is leaking underneath the shower pan from the lower corners of the shower wall. We can see moisture on the backer board when we removed the drywall from our bedroom.

A rotozip or a hand grout removal saw will work.

I'm thinking your shower pan is leaking however....

too add:

There should be a 6 mil poly sheathing behind your backerboard to make the residual water go down into the pan. Tile and grout are not waterproof, so water will get behind them.

I think that is the mistake we made. We didn't apply any sheeting behind the backer board. I guess will pull the wall down and start over. Thanks