Heat Leak Radiator

Just wondering if anyone can explain the purpose of one of these?

At the moment I'm doing UDHWS Systems in college, came across this in my book but book explains nothing.

Thanks

The function of this kind of radiator is two fold:

1) To dissipate the heat output from the boiler stove during slumbering conditions once the domestic hot water cylinder has been satisfied. This will prevent overheating of the domestic hot water supply.

2) In order to maintain combustion the appliance requires an adequate supply of air. Once the hot water cylinder (during slumbering periods) has been satisfied the appliance thermostat (if fitted to your wood-burner) will remain closed, and under these conditions the fire may “go out” due to the lack of combustion air. The heat leak radiator ensures the appliance thermostat is stimulated from time to time during any slumbering period to prevent this. Normally, the “heat leak” radiator should be installed in a bathroom as a towel rail as well as heating the room.

from http://www.frenchentree.com/france-limousin-wood-burners/displayarticle.asp?id=21700

Ahh I get it, cheers.