Doby

If your talking about a true boiler in that it heats your home as well as your domestic hot water then some times a mixing valve can be installed between the hot & cold right at the coil.

This valve is usually a "gate" valve and is used to let cold water mix in with the hot to temper it as it leaves the coil, the trick here is a gate valve can be ajusted to let as little or as much cold water enter the system as desired.