Hugh:
If you are generally a PAYE fellow and you derive a substantial amount of your income from that source and this renting is merely incidental (about less than 10%) then relax.
If you lived in this house during 2004 it might qualify for 'Rent a Room' if the total rent and all payments to you is less than €7500 per year.
That said, you may have a Case V Rental Income. Basically against the Rent you can set all related expenses including interest and a 'writing down allowance' for furniture ..and there is a list ..
Relax