Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove ST9 connector from the PCB
If available use the Worcester test PCB to assist the resistance test
If available use the Worcester test PCB to assist the resistance test
Measurement:
Test 1:
Measure the resistance between the yellow and grey wires
terminal 1 and 2 counting from left to right.
Then measure between the blue and black wires at
terminal 3 and 4 counting from left to right.
Expect approximately 177 ohms on one pair
wires and 400 ohms on the other pair.
Test 2:
Measure the resistance between each
of the black wires 1,2,3 and 4 to earth.
Expect open circuit on each test
Measure the resistance between the yellow and grey wires
terminal 1 and 2 counting from left to right.
Then measure between the blue and black wires at
terminal 3 and 4 counting from left to right.
Expect approximately 177 ohms on one pair
wires and 400 ohms on the other pair.
Test 2:
Measure the resistance between each
of the black wires 1,2,3 and 4 to earth.
Expect open circuit on each test
Isolate as per TOPs P4
and refit as necessary