The first time homebuyer credit was a credit on your Federal Income tax return. So your question is really a tax question and should be addressed to a tax professional....which I am not. However, I believe that it's a fairly simple matter to solve if you'd like to rent your property.
The 2008 tax credit was different than the similar first-time homebuyer tax credits of 2009, 2010, etc. The 2008 homebuyer credit is needs to be repaid as an additional tax on your federal tax return for fifteen years, starting with your 2010 tax return. If you received the maximum $7,500 credit, this works out to annual repayments of $500 per year. You could think of this tax credit as an interest-free 15-year loan. The credit will also need to be repaid in full if the taxpayer sells the house within the fifteen-year repayment period.
The credit also needs to be repaid in full if within 36 months of buying the property, the home is no longer the taxpayer's primary residence. However, since you've lived in the home as your primary residence for over 36 months, you merely have to continue paying your $500 a year, even if you rent it out and it is no longer your primary residence.
The way I believe it works is like this....most likely, (If you received the maximum $7,500 credit), when you filed your 2010 tax return, you repaid $500 of your credit. The same thing with your 2011return...if you've filed already. So, your current "balance" is $6500. I believe all you have to do is continue to pay $500 a year until your 2025 return.
If you mention what I've just written above, to 10 people, 9 will claim I'm nuts, but those 9 might think that the tax credits of 2008, 2009, and 2010 were all the same....they aren't.
Here's a link to more information.
My advice to you is to talk with a tax professional, but I'm pretty sure the way it works is as above.