Problems with new shower

[roythegrass]

We have a shower in the ensuite bathroom fed from a hot water tank in the airing cupboard via a pump in the loft.

We recently had the family bathroom refitted and a new shower installed with the feed T’ed off the existing pump outlet. When the new shower lever is turned on it can take several minutes for the flow to start – sometimes not at all. However if we first turn on the shower in the ensuite bathroom the new shower will start instantly. So the pump is more than capable of feeding both showers.

Any ideas as to why the new shower will not start on its own. Thanks.

 

[Madrab]

Is the distance greater? More pipe distance means more friction for the gravity flow to overcome, especially if it's going into a negative head location, therefore it's having trouble creating suitable flow for the pump to activate.

 

[roythegrass]

Hi, Thanks for that.
The pump is located in the loft directly above the new shower whilst the old ensuite shower is about 2 meters from the pump.