What is a mains pressure system boiler ?
This term refers to the pressure achieved at your hot water taps. Mains pressure systems provide
mains pressure hot water. Any system supplying mains fed is only as good as the pressure supplied to it. so there is little
point in this system if you have poor mains pressure.
There are 2 main types of domestic mains hotwater systems
Unvented mains pressure systems
In an unvented system the incoming cold mains water enters an expansion vessel where it can
be either heated indirectly by by means of a primary heating coil within the expansion cylinder which is supplied
by your central heating boiler. The hot water stored is forced out by by the incoming cold mains pressure water when a tap
is opened. Hence the name mains hot water. The expansion vessel can also be heated directly by an electric heater although
this is the less common option.
Vented mains pressure systems.
In a vented mains pressure system the heating cylinder has its own secondary heat exchanger.
The cylinder stores hot water which inturn heats up the the incoming mains cold water which passes through the heat exchanger
the temperature in the store is maintained either directly by heaters or indirectly by the central heating boiler.
Examples of vented and unvented cylinders.
