Look in the TV's menu to change the country to Ireland. On my Samsung press "menu" on the remote then select "channel" and then "country". From there select "Ireland". Then select "auto tuning" within the "channel" menu.
How old is the TV? Ireland uses MPEG 4 for SD channels whereas the UK uses MPEG 2. Newer TVs will handle MPEG 4. Best thing is to try and see, if TV is MPEG 2 only you will get sound but no picture. If this is the case buy a Saorview box, around €40 I think.