Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove electrode assembly from boiler
Disconnect lead from the PCB

Measurement:

Thoroughly check the spark electrode for wear, contamination,
cracks and damage, confirm electrode gap is 4mm +0.5mm.
Measure the resistance of the electrode and lead, from the tip of
the electrode to the lead connector.
Also visually inspect the condition of the lead.
Expected resistance approx. 5Kohms.