Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Gain access to internal programmer terminal block
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Ensure internal programmer is calling for heat.
Test 1:
Measure voltage across terminal 1 (top terminal, Red wire) and neutral marked N (terminal 5,blue wire) at the terminal block.
Test 2:
Measure voltage across terminal 2 (red wire) and Neutral
marked N (terminal 5,blue wire) at the terminal block.
Is mains voltage present on both tests?