Raypak B0507, Owner'S Manual And Installation Instructions, Page: 7 / 57

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 to ensure efficient operation of the water heater. The refractory tiles insulate
the combustion chamber to minimise heat loss and protect the surroundings from the temperature of the burner
flames. The gas supply to the burner is controlled by an electronic thermostat which senses the water temperature.
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 are normally connected directly to the mains water supply. If the mains water supply pressure
in your area exceeds the value shown in the
“Pressure Specifications”
table on page 14 or exceeds the specified
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
“Pressure Specifications”
table on page 14 .
ELECTRONIC THERMOSTAT (ON/OFF MODELS)
On/Off models are fitted with an IC902 electronic thermostat that operates the gas control by switching its power on
and off so that a constant temperature is maintained. The electronic thermostat is mounted on the control panel of
the water heater and the protective over temperature cut out (high limit thermostat) is mounted inside the lower
front cover of the water heater.
There is no need to switch the water heater off when it is not in use. The electronic thermostat is fully automatic
and only allows the gas control to open when the burner requires gas for heating.
The electronic thermostat has a number of parameters that are programmed during manufacture. To adjust the
parameter settings refer to
“Temperature Adjustment – On/Off Models (IC902 Electronic Thermostat)”
on page 43 .
Warning: Advice should be sought from your local Raypak representative prior to altering any electronic
thermostat values other than the set point or differential.
ELECTRONIC THERMOSTAT (MODULATING MODELS)
Water heaters with modulating operation are fitted with an RWF55 electronic thermostat. The electronic thermostat
is mounted on the control panel of the water heater and the protective over temperature cut out (high limit
thermostat) is mounted inside the lower front cover of the water heater. This type of thermostat is used where the
system load is variable e.g. Mechanical Heating. The RWF55 electronic thermostat will cycle the burner from full
fire to 30% and then off.
There is no need to switch the water heater off when it is not in use. The electronic thermostat is fully automatic
and only allows the gas control to open when the burner requires gas for heating.
The electronic thermostat has a number of parameters that are programmed during manufacture. To adjust the
parameter settings refer to
“Temperature Adjustment – Modulating Models (RWF55 Electronic Thermostat)”
on
page 46 .
Warning: Advice should be sort from your local Raypak representative prior to altering any electronic
thermostat parameters other than the set point or differentials.
BURNER IGNITION
The water heater incorporates an automatic burner ignition system and an automatic pilot burner. The pilot burner
ignites the main burner gas when the electronic thermostat determines a need for heating.
Both On/Off and modulating models have a spark generator that begins operating when power is applied and any
external controls (if installed) call for the water heater to operate. At the same time a valve opens to supply gas to
the pilot burner. After successful ignition of the pilot flame has been detected, the valves open to supply gas to the
main burner when the electronic thermostat determines that a call for heating is required. If the pilot fails to ignite
within 5 seconds, the ignition system will lock out.