The good news with wet underfloor heating is that the pipework will never leak if it is of good quality and has been pressure tested. Make sure the pipework is made to the highest quality possible, by a manufacturer such as Henco (www.henco.be). A reputable company will test every mm of the pipe before it is sold.
If there are any issues with the heating system, it is usually due to incorrect wiring or possibly a leak in one of the manifold connections, which is very easy to repair.
If the pipe is damaged accidentally by a builder drilling into it, this can be fixed by taking up the floor boards and removing the screed around the pipe. Finally, a coupler can be fitted where the leak is, to cover the damaged area. It is important to use Denso tape around the couplers, to prevent it from reacting with the screed.
You may find that house insurance will cover the cost of fixing any damage to the pipe. This of course depends on the particular policy.
Another risk factor could be freezing outside air temperatures. Make sure that the property is air tight, i.e. roof, windows, doors and walls are all fitted before the underfloor heating is installed.
Underfloor heating systems are normally pressure tested with water and it is normal practice to leave this water in the pipework after the system has been installed, therefore there is always a risk that the water will freeze if the outside air temperature drops below zero. Take care to protect the pipework and manifolds against frost.