Some AIB mortgage contracts, and maybe some others, allow you to return to your tracker after fixing
In most cases, when you fix, you lose your right to your tracker. But if your mortgage contract is crystal clear, then you could consider fixing. But it must be crystal clear and the margin must be specified "At the end of any fixed rate period, you will have the option of returning to the tracker rate specified in Condition... " Get it in writing from your lender that you can return to this actual rate. Some contracts say "You will be offered a tracker at the then prevailing rate" . That is no good to you, as the prevailing margin at that time, may well be 3.5%.