Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Gain access to PCB (use Insulation Mat as required)
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Reset appliance if required
(press and hold the reset button for 4 seconds then release)
Monitor the DC voltage across the blue wire on connector X21 and an earth (use the copper pipe to the gas valve as earth) while the appliance operates.
Before the burner ignites approximately 0V DC will be present, once the burner has ignited the voltage should change to -10V to -35V DC (this is the rectification voltage) while the appliance runs.
Does the voltage behave as described?
(press and hold the reset button for 4 seconds then release)
Monitor the DC voltage across the blue wire on connector X21 and an earth (use the copper pipe to the gas valve as earth) while the appliance operates.
Before the burner ignites approximately 0V DC will be present, once the burner has ignited the voltage should change to -10V to -35V DC (this is the rectification voltage) while the appliance runs.
Does the voltage behave as described?
Isolate as per TOPs P4
and refit as necessary