I have a DC25 that has just started with the following fault. In the unright position the van is working ok with sucktion. When you try to use the van in the normal push position the motor isnt kicking up. I took off the head and checked everything and the belt is ok and also the motor is ok. I quickly put it back on before screwing it back together and it kicked up. So put the screws back in and the vac worked for aroud 5 second and then the same. It seems that there is a switch of some type when you put the vac into the push position that just isnt working. Can anyone help? what to look for or where to look etc?