Unless your mortgage is very small or you own the property outright your not gonna make much money on it now, its a long term venture for capital increase on the value (Future sale value).
As a landlord you want a property that you can buy with a mortgage and rent easily and also to make sure the rental covers the mortgage and gives you some money left over (Yield), if your getting 4-8% yield your doing ok, anything over that your doing well, plus long term you have possibility for increased property value, As we all know values on properties can go down (It happened already!), but as someone is paying it for you anyway your still not losing out!
The way you look at it is someone else is paying your mortgage and giving you the "Chance" of increased sale value in the future plus also paying your debt on the property, so nto effectively costing you money, plus when the mortgage is paid your making money on it then with rental income.
Had a client year back who had over 400 properties, made very little in the way of profit at the time (he used the excess income to re-decorate/new bathroom/kitchens etc to increase value of properties and keep them looking nice for tenants (nice looking/well fitted out properties rent quicker/easier), he will make some serious money in another 15 years when he retires and mortgages are paid off, all rental income is profit then, but he will be clobbered for capital gains on sale of them (although someone else has paid for them really so he did not see it as an issue paying 20-30% of his profit in tax)..............
Got a couple of my mates doing property development currently, aside from their full time jobs (Both single and live at home with parents), they do 2 properties each a year on average (1 of them will do 3 houses this year), its their only house so no capital gains to pay, another 3 years and one of them reckons he will have enough to buy his own place outright (cash purchase), not bad for a 26 year old
something I should have done myself!
If I was doing it myself I would ensure mortgages were paid off when I am ready for retiring and use the income as part of my pension, if you have several properties you can always sell off one or 2 to give you that "lump sum" to buy a boat/nice car/retirement home etc
Someone else mentioned the council letting it, housing companies do this too, you get less back but you do get guaranteed monthly income, its all risk and what your prepared to do.