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7
HOW YOUR WATER HEATER WORKS
The water heater consists of a gas burner, a combustion chamber lined with refractory tiles and a heat-exchanger
made of finned copper tubes. Hot flue gases from the burner pass between the fins on the heat exchanger tubes
and heat is transferred first to the fins and then by conduction into the water. Baffles are placed between the tubes
to control the flow of the hot flue gases and ensure efficient operation of the water heater. The refractory tiles
insulate the combustion chamber to minimise loss of heat and protect the surroundings from the temperature of the
burner flames. The gas supply to the burner is controlled by a thermostat, which senses the temperature of the
water.
Automatic safety controls are fitted to the water heater:
• to ensure safe ignition of the gas whenever there is a call for heating;
• to continuously monitor the burner flame; and
• to prevent excessive temperatures or pressures in the water system.
MAINS PRESSURE
In water heating applications, the water heater is designed to operate in conjunction with one or more hot water
storage tanks, which would be connected directly to the mains water supply. If the mains supply pressure in your
area exceeds the value shown in the table on page 15 or the maximum inlet pressure for the storage tanks, a
pressure limiting valve must be fitted.
In mechanical and process heating applications, the system pressure must not exceed the value shown in the table
on page 15.
109 MODELS
On/Off Operation
109 On/Off models are fitted with a mechanical thermostat, adjustable from 0°C to 95°C that
operates the gas control by switching its power on and off, so a constant temperature is
maintained. The thermostat and the protective over temperature cut out are mounted on the
control panel which is located behind the lower front cover of the water heater (refer to
"Location of Controls"
on page 29).
There is no need to switch the water heater off when it is not in use. The thermostat is fully
automatic and only allows the gas control to open when the burner requires gas for heating. To adjust the
thermostat settings refer to “Temperature Control
” on page 35.
Hi/Lo Operation
109 Hi/Lo models are fitted with a mechanical thermostat, adjustable from 45°C - 85°C that
operates the gas control by switching its power from high fire to low fire and off, so a constant
temperature is maintained. The thermostat and the protective over temperature cut out are
mounted on the control panel which is located behind the lower front cover of the water heater
(refer to "Location of Controls"
on page 29).
There is no need to switch the water heater off when it is not in use. The thermostat is fully
automatic and only allows the gas control to open when the burner requires gas for heating. To adjust the
thermostat settings refer to “Temperature Control
” on page 35.