Dear expert modelers~

I have bought the Pro-Spray MK IV to spray large area and its ease of colour change. Unfortunately this pen don't  know why its top trigger doesn't work anymore, the pen just keep spraying unless I adjust its airflow by turning the back ring. Did anyone know why?
I currently have a sparkman BRH 3003 but I REALLY don't like to use that since I always have to wash it before colour change and I hate to wash it.....

Thanks everyone!!! I will learn to type chinese later~

Here is the pic of this product