A conventional boiler is a water heater that indirectly heats up water through a hot water cylinder, and provides heating to radiators, ufh etc. Normally this type of boiler and system setup will have a hot water cylinder and tanks in the loft, this provides gravity hot water and gravity heating, normally you will have an airing cupboard which will house your cylinder, pump, motorised valve and main heating junction box.

The advantages of a conventional boiler

that the pipe work is under less pressure and any parts that need replacing are normally external to the boiler and easily accessible.

The disadvantage to this type of system

because the system is open to the atmosphere through the open vent and expansion, this can drag air in and cause corrosion inside the radiators and pipe work. Also, generally the hot water pressure is not normally great and suffers even more when people upgrade there bathroom or kitchen with modern taps which are designed for mains pressure so massively restricts flow.