1. If I don't live in my house any more is it now an investment property and will the bank take me off my tracker morgage?
Yes, it becomes an investment property. You'll need to check the terms and conditions of your mortgage letter of offer - some require you to notify any change in status, others don't. If you don't still have that, call your lender to check - and get the answer in writing.
2. when renting out my house do i need to change my house insurance?
Yes. You won't be covered by owner-occupier insurance.
3. Has anyone ever done this and do they know about any of the pit falls?
Haven't done it, but off the top of my head -
Remember you cannot claim mortgage interest relief when you're no longer an owner occupier.
You will be liable for tax on any profit rent. Previously, that's been rent minus the interest portion of the mortgage (and
only the interest portion), insurance, depreciation on furniture and fittings, and other associated expenses (repairs, management fees and the like).
You may have to pay stamp duty if you received a stamp duty exemption and you rent out the house within two years.
There's also the general hassle of being a landlord, getting tenants, ensuring the house is maintained and all of that. It's taking longer to let places and rents are falling - do factor that in when working out if you can afford this.