Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to AC Volts 
DHW Demand
Gain access to PCB (use insulation mat as required)
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure the voltage on the left hand terminal block between the connections marked "SL2 IN" and "N".
With a DHW demand mains voltage should be absent.
Note:
Voltage on SL2 is supplied by the HW OFF
at the cylinder thermostat / timer.
With a DHW demand mains voltage should be absent.
Note:
Voltage on SL2 is supplied by the HW OFF
at the cylinder thermostat / timer.
Isolate as per TOPs P4
and refit as necessary