The combination central heating boiler is basically a central heating boiler which becomes an instantaneous multipoint water heater when there is a demand for domestic hot water.
Most combination boilers use a gas to water heat exchanger where the heat from the main gas burner is used to heat the water contained within the water ways of the heat exchanger.
A calorifier is a water to water heat exchanger which consists of a tightly wound
copper coil fitted within a cylindrical casing. The tightly wound coil typically
consists of 20 feet of 12mm copper tubing and as the domestic-hot water passes
through it picks up heat from the surrounding hot water on the outside of the coil
and within the cylindrical reservoir.
On the more recent combination boilers the design of calorifier has been updated and changed. The earlier design of a closely coiled tube has been replaced by a plated heat exchanger design. In this type of calorifier the heating water and domestic hot water runs across alternative plates within the heat exchanger and there by transfers heat from the boiler into the domestic hot water. These type of heat exchangers are more efficient and reliable than earlier ones.
This type of heat exchanger consists of two tubes one inside the other. When the boiler heats up, the heat from the outer tube is transferred to the inner tube containing the domestic hot water and so no separate calorifier is required for this type of system as the boiler water and the domestic hot water are kept separate at all times.
The combination central heating boiler is basically a central heating boiler which becomes an instantaneous multipoint water heater when there is a demand for domestic hot water. Although the basic principle is the same for all combination boilers there are various different methods used to obtain the production of hot water, dependent on the manufacturer.
The four basic designs are:
Utilising heat exchanger, diverter valve and calorifier.
Hot Water Mode
The operation of the domestic hot water draw off tap leads to the mechanical movement of the diverter valve and the change of operation of the boiler to that of an instantaneous water heater.
Utilising single heat exchanger and diverter valve.
Hot water mode
The operation of the domestic hot water draw off tap again leads to the mechanical movement of the diverter valve but due to the design of the main heat exchanger does not require a second heat exchanger (Calorifier)
The operation of the domestic hot water tap causes the main burner to light and heat the water in the main heat exchanger and transfer its heat to the domestic hot water without the need for the use of either a pump on a second heat exchanger (Calorifier).
Hot water mode
This type utilises 2 pumps, one runs on operation of domestic hot water tap the other on demand for central heating. Each pump contains a nonreturn valve to prevent reversed circulation within the boiler when the opposite pump is running.
Hot water mode