for two different things, you also have a room stat as well, 3 different temp settings? and one on each of your radiators? 10 temp settings in your average house, obviously they all control different things
TRV: Sets the temp of the room at which the connected rad will shut off.
Room stat: Sets the temp of the room at which the heating will shut off.
Cylinder Stat: Sets the temp of the DHW (at which it will stop calling for heat, & send power to the DHW off terminal of your 3 way valve)
Boiler Stat: Sets the temp of the water inside the central heating system, the actual radiator temp.
intersimi: it may be an idea to turn your boiler stat to 70, if the problem continues with no further sympoms it may be wise to change your boiler stat
mickeyw: Combi? sounds like you either have a proplem on a sensor or your flow switch isn't reseting fast enough. I am not familier with your boiler, if you have a facility to turn down the temp of the hot water do it, and see if it helps, is it actually shutting off while you are still running the tap or after you turn the tap off?