Step on habitation door not workinf

The electric step on the habitation door does not close and the warning buzzer keeps on buzzing. Has anyone any ideas please. Thank you.

Thank you

Does the step not close automatically when the engine is started ?
Or does it not close when you use the manually operated switch ?
Or both ?
I suspect the limit switch inside the step but an answer to the above would help diagnosis.
Keith

You could find its a build up of dirt from the roads preventing it from sliding all the way back.

Step on my 2010 Broadway occasionally wouldn't fold back. Seemed to be particularly after rain and on checking wiring to step I found that the flexible tubing covering the wiring had broken just short of entering the control box at the step. Taped this with insulating and step working OK in all conditions. Can only assume cause was dampness/water entering control box through break.

This happened from time to time on my Nuevo. If you look underneath at the back of the step it does collect a lot of dirt.
I used to give it a good clean with a stiff brush. There is a spring loaded switch at the back of the step enclosed in a rubber cover. If you push this a few times and give it a spray with silicone that used to get it working again. 
On its last habitation check before I sold it the step played up again. 
My local dealer removed the switch and gave it all a good clean and it was as good as new again.

I mentioned the problems I was having with the step on my Rienza, not retracting when the ignition is on. It is in the technical help section.