What is an Ignition Unit?
An Ignition Unit is an electrical part within the boiler that works with the PCB to ignite the burner. When the Ignition Unit receives a signal from the PCB it will generate a high voltage pulse which is then sent and creates a spark at the spark electrode. A boiler may have a Piezo as the spark generator where the ignition is manually done by pressing a button. It is very common for the manufacturers to name the Ignition Unit differently, see the following examples
Alpha - Spark Generator
Baxi - Igniter or Spark Generator
Glowworm - Transformer, Igniter or Spark Generator
Ideal - Igniter Unit or Spark Generator
Vokera - Ignition Box