my mira shower stops in the middle of a shower?

When im showering after a few minutes my mira elite st stops working as if it runs out of water, I have checked the water supply and the tank has plenty of water. I took off the face of the unit and cleaned the filter and took off the hose's to make sure their not blocked. everything seems ok. then leave it for an hour and it will work for another few minutes. any help would be appreciated