Handle has come loose, just spins. - Moen 3175 Legend One Handle Shower Faucet With trol Pressure Balancing Valve....

Look underneath.
Turn handle loose to shaft? Shaft mot spinning.
Loose nut/bolt shaft disconnected from gear.
Was dropped, gear broken.
Belt broken?

If you can turn the handle and there is resistance but it turns. You probably had a bolt come undone.

It seems that your handle is either stripped or become loose. You are going to have to remove the "concealing cap" on the very end. This can be removed carefully with a small flathead screwdriver. After removal you will see a screw in the center. WHen you spin the on/off does the screw turn at the same speed as the on/off? If it is not spinning then tighten it and see if this solves your problem. If not, more information is required than what was given. The owners manualk for your bar is available here:
http://www.mirashowers.co.uk/onlinecatalog/pdf/1196840_w2_a_mira_reflex_bar_valve.pdf

Good luck!

When the blades are engaged do they turn? It could be a belt is loose tha causes the blades not to spin. Check the handle that engages the mower deck to see if it goes into the proper slot which would cause the blades to spin.

Remove lock from door.The round part contacting door usually spins to accommodate different width doors. This will pull the assembly together.

seems like theres a bad contact there must be the switch when you have it up its working and when you bring it down looses contact

sounds like a clutch problem worn out not able to handle the heavy load!

The brush roll will only spin when your handle is not in the locked upright position, once the handle goes upright - the brushroll de-activates

it might be the drive belt slipping if the unit is off then the belt is locked onto the belt and then when the unit is switched on the belt slips and if its loose it doesnt hold the belt to the motor shaft 

the set screw in the handle is not tight enough. I suggest you remove handle, remove set scew, clean and lube set screw, re install screw and fully run in and out several times. THEN out it back on the faucet ball stem.

I pulled the handle out until it was past the cartridge jacket then sawed the handle and the screw in half. I found that the plastic portion of the handle that holds the cartidge was broken, hence the reason the screw felt loose.