Specifications

TM002 Integrity 18 & 20L Service Instructions REV: E

D.O.I: 7/11/2007

This document is stored and maintained electronically by Service. All printed copies not bearing this statement in RED are deemed “uncontrolled”

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 model heaters fitted with a comparator the inlet

water temperature must be less than or equal to 57ºC and for 871020-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 11).

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.