Problem with twin shower one pump set up

[lloydfoulds]

Hello all, I have two showers on a 3.5 bar twin prop pump. When the 2nd shower is turned on the first shower will operate. When both showers are running the pressure is fine.

Why wont the 1st shower operate the pump alone. Why doesn't the pump detect the pressure drop and activate from the 1st shower?

Any help please.

 

[muggles]

Are the showers different or the same? Are they at the same height in the house?

 

[lloydfoulds]

Are the showers different or the same? Are they at the same height in the house?

Yes they are at the same height in the flat.