Do I have a problem with Baxi Solo 15 HE do I need an engineer

[PaulDDrabble]

Hi, we have a Baxi Solo 15 HE condensing boiler - The wall timer for the Central Heating and Hot Water is set to OFF not via the timed on off system, yet the boiler seems to switch on approximately every 10 Mins and runs for between 30 seconds and a minute.
When I say switch on, I can hear the boiler fire up and then a humming noise like a pump or a fan and the 'Burner On' green light comes on.
I can interrupt this process by turning down the boilers black 'Central Heating control' knob to 1/4
Can any engineers tell me is this normal or is there a fault please?

 

[SJB060685]

I suspect initially this is a failed HW two port valve?
Whatever the case I would hire a gas safe registered technician.