If the door has locked the first thing it is going to do is call for water -Hot first on any programme 40degrees or above -has the valve gone -you can usually hear a slight hum but no water going in or the most common reason I get is someone has turned off the tap.
The start light just flashes and nothing happens after the programme has been selected and the on/off switched on.
Chris.
By that statement I would glean that its more or less an instant thing the start light flashing.
I would put money on interlock, shame Chris hasn’t got back with flash count as Boro rightly asked for.