I have a 3 month old normal mains fed electric shower (Triton Cara ) and live in the 3rd floor of a flat.All of a sudden in the mornings the water will suddenly turn cold and the pressure decrease. This hasnever happened before. I had the water pressure checked out by Thames water and the said the water was 2 bar so a good flow. I notice when i unscrew the shower head from the hose though and turn the shower on the water stream will move up and down!
The cold water and low pressure occurs at peak times thought the strange flow of the shower is always notceable.
What is the best way to deal with this, install a pump, or should I install a thermostatic shower or a power shower?
I have a very small hot water tank, but it is not an overhead tank

Many thanks for your help!