7
Sequence of Operation
Refer to „Sequence of Operation Component Diagram‟ on page 9 to view components
shown in brackets e.g. (1)
1. When a hot water tap (1) is opened, cold water (or preheated water if a solar preheater
is installed) enters the water heater and passes through the Water Flow Sensor (3) and
Heat Exchanger (19). Note: For 871020, 871024, 871024-B, and 871026 model
heaters fitted with a comparator the inlet water temperature must be less than or equal
to 57ºC and for 871020-B, 871024-C and 871026-B models the inlet water temperature
must be less than or equal to 58ºC and less than or equal to the set point temperature
minus 2ºC for operation to occur past this point; otherwise water will pass straight
through the heat exchanger and fan and burner operation will not occur (for more
information on this subject refer to the section titled „In-series Gas Boosting‟ on page
15).
2. The Water Flow Sensor (3) sends a pulse signal to the PCB (27). Once the pulse
signal reaches a pre designated frequency (at minimum flow rate) the PCB (27)
activates the Fan Motor (25) and the Fan (24) starts rotating.
3. After the Fan (24) completes a pre purge, the Gas Inlet Solenoid Valve (9), Gas
Solenoid Valve 1 (10) and Gas Solenoid Valve 2 (11) open at the same time. The
Proportional Gas Flow Regulating Valve (13) adjusts the gas flow rate to ensure
adequate gas for ignition and gas is then supplied to the Burner (15).
4. At the same time the Gas Solenoid Valves open the Igniter (16) starts sparking
continuously and ignites the gas at the Burner (15). After the flame sensor (18) detects
burner flame, the Proportional Gas Valve (13) begins to control the gas flow rate. If
there is a difference between the hot water temperature detected by the Hot Water
Outlet Thermistor (6) and that set on the water heater or selected on the remote
controller (if fitted) the PCB (27) adjusts the hot water temperature by opening and
closing the Gas Solenoid Valves 1 (10), 2 (11) and 3 (12) and adjusting the
Proportional Gas Flow Regulating Valve (13). The water flow rate is also adjusted via
the Water Flow Servo Motor (7) to ensure the selected temperature of hot water is
delivered.
5. As the gas flow rate, controlled by the Proportional Gas Flow Regulating Valve (13)
changes the PCB (27) varies the speed of the Fan Motor (25) to maintain the correct air
gas mix ratio.
6. When the hot tap (1) is closed, the pulse signal from the Water Flow Sensor (3) stops
and the burner flame is extinguished by closing Gas Solenoid Valves 1 (10), 2 (11), 3
(12) and the Gas Inlet Solenoid Valve (9). The post purge operation then commences.
7. Once the post-purge operation ends (up to 6 minutes) power to the Fan Motor (25) is
cut and the Fan (24) stops.
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