Specifications

TM040 16, 18 & 20L Continuous Flow Gas Water Heater Service Instructions
D.O.I: 2/06/2009
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8
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 pre-
heater is installed) enters the water heater and passes through the Water Flow Sensor
(3) and Heat Exchanger (18). Note: 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 10).
2. The Water Flow Sensor (3) sends a pulse signal to the PCB (7). Once the pulse signal
reaches a pre designated frequency (at a min. flow rate of 2.5lpm) the PCB (7)
activates the Fan Motor (24) and the Fan (23) starts rotating.
3. After the Fan (23) 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 (12) adjusts the gas flow rate to ensure
adequate gas for ignition and gas is then supplied to the Burner (14).
4. At the same time the Gas Solenoid Valves open the Igniter (15) starts sparking
continuously and ignites the gas at the Burner (14). After the flame sensor (17) detects
burner flame, the Proportional Gas Valve (12) 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 controller (if
fitted) the PCB (7) adjusts the hot water temperature by opening and closing the Gas
Solenoid Valve 1 (10), the Gas Solenoid Valve 2 (11) and the Proportional Gas Flow
Regulating Valve (12). The water flow rate is also adjusted via the Water Flow Servo
Motor (2) to ensure the selected temperature of hot water is delivered.
5. As the gas flow rate, controlled by the Proportional Gas Flow Regulating Valve (12)
changes, the PCB (7) varies the speed of the Fan Motor (24) 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), 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 (24) is
cut and the Fan (23) stops.