Also look at the what, if any, net gain you will have. If you get €1000 per month in rent that's €10'000 per year allowing for empty times and expenses. I don't know what your tax situation is but if you pay 1/4 of the income in tax (allowing for mortgage interest relief etc) you will need to clear about €150'000 that can be taken off your mortgage to justify the loss of income.
As Brendan pointed out you will also have to pay transaction costs such as CGT, legal fees, estate agent fees etc. On a house that you sell for 350k that you bought for 100k even allowing for the years when there was indexation you will pay around (ballpark) €40’000 in CGT. So that’s 50 odd thousand to sell up and the loss of rental income in a low interest environment.
I’m not saying don’t sell I’m just agreeing with Brendan that it's not cheap to get out of the rental business so make sure you do the figures before you put up the foe sale sign.